STAHL, Circuit Judge.
Following a lengthy criminal trial, a jury convicted defendant Alfred Trenkler of various charges stemming from a bomb explosion in Roslindale, Massachusetts (“the Roslindale bomb”). On appeal, Trenkler challenges the admission of evidence relating to his participation in a prior bombing that occurred five years earlier in Quincy, Massachusetts (“the Quincy bomb”). Trenkler also assigns error to two evidentiary rulings admitting evidence derived from a computer database that purported to establish that Trenkler built both the Quincy and the Roslindale bombs and several out-of-court statements made by a fellow participant in the bombing. After careful review, we affirm.
I.
Background
On October 28, 1991, a bomb exploded at the Roslindale home of Thomas L. Shay (“Shay Sr”), killing one Boston police officer and severely injuring another. The two officers, members of the Boston Police Department Bomb Squad, had been dispatched to Shay Sr.’s home to investigate a suspicious object located in Shay Sr.’s driveway. Shay Sr. had earlier reported that, while backing his 1986 Buick Century into the street the day before, he had heard a loud noise emanating from beneath the floorboard of his [48]*48automobile. Shay Sr. added that, subsequently, he found the suspicious object resting near the crest of his driveway.
Following the explosion, a massive investigation ensued involving a variety of federal, state and local law-enforcement agencies. On June 24,1993, this investigation culminated with the return of a three-count indictment charging Trenkler and Thomas A. Shay (“Shay Jr.”), Shay Sr.’s son, with responsibility for the Roslindale bombing.1 Trenkler filed a successful severance motion, and the government tried the two defendants separately. Shay Jr. was tried first, and a jury convicted him on counts of conspiracy and malicious destruction of property by means of explosives.2
At Trenkler’s trial, the thrust of the government’s ease was that Trenkler had built the Roslindale bomb for Shay Jr. to use against his father. To establish Trenkler’s identity as the builder of the bomb, the government offered, inter alia, evidence that Trenkler had previously constructed a remote-control device, the Quincy bomb, which exploded in Quincy, Massachusetts, in 1986. The government contended that unique similarities in design, choice of components, and overall modus operandi between the two bombs compelled the conclusion that Trenk-ler had designed and built both devices. Pri- or to trial, the government filed a motion in limine seeking to admit the “similarity” evidence. Following a day-long evidentiary hearing, the district court ruled the evidence admissible, finding that it was relevant on the issues of identity, skill, knowledge, and intent. Although Trenkler did not testify at trial, his counsel stipulated at the evidentiary hearing that Trenkler had built the Quincy bomb.3
1986 Quincy Bomb
Trenkler constructed the Quincy bomb in 1986 for a friend, Donna Shea. At the time, Shea was involved in a dispute with the owners of the Capeway Fish Market and she wanted the bomb to use as a means to intimidate them. At her request, Trenkler assembled a remote-control, radio-activated explosive device. The device was later attached to the undercarriage of a truck belonging to the Capeway Fish Market and detonated in the middle of the night. The resulting bomb blast caused no injuries and little property damage.
In building the Quincy bomb, Trenkler used as the explosive material a military flash simulator typically utilized to mimic gunfire in combat exercises. To provide remote-control capabilities, Trenkler employed a radio-receiver he had removed from a small toy car. Trenkler wrapped the bomb in duct tape and attached a large donut-shaped speaker magnet to enable the bomb to adhere to the undercarriage of the truck. Other components Trenkler used included a “double throw” toggle switch, four AA batteries, two six-volt batteries, an electric relay, solder, various wires, and a slide switch.
Testimony at trial established that Trenk-ler purchased some of the electrical components for the Quincy bomb from a Radio Shack store. On one occasion, Trenkler sought to obtain needed components by sending Shea’s eleven-year-old nephew into a Radio Shack store with a list of items to purchase while Trenkler remained waiting outside. Shea’s nephew, however, was unable to find all of the items, and Trenkler eventually came into the store to assist him.
1991 Roslindale Bomb
The government contended that Trenkler built the Roslindale bomb at Shay Jr.’s re[49]*49quest. At trial, the government offered evidence about Trenkler’s relationship with Shay Jr., dating back at least two years prior to the Roslindale bombing. Several witnesses, including Trenkler’s business partner, reported seeing the two together on different occasions in 1990 and 1991. Shay Jr.’s address book included an entry for Trenkler listing his current pager number. Moreover, Trenkler’s roommate at the time of the Roslindale bombing testified that, during September and October of 1991, Shay Jr. left several voice-mail messages on the pager for Trenkler.
Testimony from government investigators and Shay Sr. established that the Roslindale bomb was a remote-control, radio-activated device with an explosive force supplied by two or three sticks of dynamite connected to two electrical blasting caps. A black wooden box weighing two or three pounds and measuring approximately eight- to ten-inches long, five- to six-inches wide and one- to two-inches deep housed the bomb. A large do-nut-shaped magnet and several smaller round magnets attached to the box were used to secure the device to the underside of Shay Sr.’s automobile. Other components used in the construction of the bomb included duct tape, a “single throw” toggle switch, four AA batteries, five nine-volt batteries, a Futaba radio receiver, solder, various wires, and a slide switch.
According to the government’s experts and Shay Sr., the bomb was originally attached to the undercarriage of Shay Sr.’s automobile directly beneath the driver’s seat. The government’s explosives expert testified that if the bomb had exploded while still attached to the car, it probably would have killed or at least seriously injured any individual sitting in the driver’s seat.
The government also asserted that Trenk-ler used Shay Jr. to purchase the electronic components used in the bomb. In support of this assertion, the government introduced a sales receipt for a toggle switch purchased in October 1991 at a Radio Shack store located across the street from where Trenkler, at the time, was installing a satellite dish.4 Agents from the Bureau of Alcohol, Tobacco and Firearms (“ATF”) recovered from the debris of the Roslindale bomb a switch identical to the one purchased. Shay Jr. admitted purchasing the switch during a taped television interview, portions of which the government introduced at trial.5 Furthermore, a sales clerk at the Radio Shack testified that, prior to purchasing the switch, the person who bought it had browsed in the store for several minutes, appearing to shop for items written on a list. The sales clerk also testified that he recalled seeing Trenkler in the store on two or three occasions during the fall of 1991.
Both the government and Trenkler elicited testimony from their respective explosives experts explaining the similarities and differences between the two bombs. Both experts testified at length concerning the electronic designs, the choice of components and the method of construction. The government’s expert opined that the two incidents shared many similar traits and characteristics, evincing the “signature” of a single bomb maker. He further stated that he had no doubt “whatsoever” that the same person built both bombs. Trenkler’s expert, on the other hand, stated that too many dissimilarities existed to conclude that the same person built both bombs. Moreover, Trenkler’s expert testified that the similarities that existed lacked sufficient distinguishing qualities to identify the two bombs as the handiwork of a specific individual.
EXIS Computer Database Evidence
To support the inference that Trenkler built both bombs, the government offered testimony both at the pretrial hearing and at trial concerning information retrieved from [50]*50an ATF computer database of explosives and arson incidents. Stephen Scheid, an Intelligence Research Specialist with ATF, testified that the database, known as EXIS, contains information taken from reports submitted to ATF by various federal, state and local law-enforcement agencies. Scheid further testified that he had been personally responsible for maintaining the database since 1977. Scheid stated that he reviews submitted incident reports, culling from them information describing the characteristics of each bombing or arson episode. Scheid added that he then encodes the extracted information on a standardized worksheet, which he or a data-entry person in turn uses to enter the information into the database.
Scheid testified that, through the use of a computer program, he then produces investigatory leads by retrieving all incidents entered in the database that are listed as possessing a specific component or characteristic. Scheid further testified that, in an effort to identify the builder of the Roslindale bomb, he performed a series of computer queries, focusing on characteristics of the Roslindale bomb. This series of inquiries narrowed the field of reported incidents in the database from 40,867 to seven.6 The seven remaining incidents included both the Roslindale and Quincy bombs. Scheid stated that he subsequently conducted a manual analysis of the remaining incidents and was able to identify several additional characteristics common to only the Roslindale and Quincy bombs.7
Scheid also testified that the report of the Quincy bomb did not come to his attention through normal procedures. Scheid did not receive information about the 1986 Quincy bomb, nor enter any information pertaining to it into the EXIS database, until after the Roslindale incident in 1991.8
Other Trial Evidence
The government also offered the testimony of David Lindholm to establish that Trenkler had built the Roslindale bomb. Lindholm testified that he met Trenkler at the Plymouth House of Correction where they had spent four days incarcerated together in an uncomfortable orientation holding cell in December 1992. Lindholm testified that initially the cell had held about forty-four prisoners, but that eventually the total number of prisoners in the cell dwindled to six or seven. Lindholm added that he had numerous conversations with Trenkler over the course of the four days as they gradually “bonded” upon discovering that they came from the same home town and had similar backgrounds.
Lindholm testified that he gave Trenkler legal advice based on his own experience as a criminal defendant. Lindholm acknowledged that Trenkler initially asserted his innocence and had maintained that he could not understand why Shay Jr. had implicated him in the case. Lindholm testified further that Trenk-ler later told him that the government knew that some of the components used in the Roslindale bomb had been purchased locally and that, in response, Lindholm opined that the bomber had been careless not to have gone out of state. To this, Trenkler agreed and then stated that the local purchase was “regrettable.”
In addition, Lindholm recalled that at one point during the four days they discussed Trenkler’s involvement with the 1986 Quincy [51]*51bomb. Lindholm testified that, during this discussion, Trenkler asserted that the Roslin-dale bomb was much more powerful than the bomb he had built in 1986. Ultimately, Lin-dholm stated that Trenkler admitted building the Roslindale bomb, testifying that:
[Lindholm:] At one point he stated, [“W]ell, even if I did build a bomb, I did not place it on the car.[”]
[Government:] What happened next?
[Lindholm:] Then he paused for a moment and said, [“S]o, I built the bomb. I built the bomb. I don’t deserve to die or spend the rest of my life in prison for building this device. [”]
Lindholm added further that Trenkler “stated that the two bomb squad officers were foolish and negligent for not wearing body armor at the time that they were examining this device, and in essence that it served them right for what happened to them. It wasn’t his fault.”
At the time of trial, Lindholm was serving sentences stemming from convictions on federal drug and tax evasion charges. Lin-dholm testified that he had not received nor discussed receiving anything fi*om the government in return for his testimony. On cross examination, Trenkler’s counsel made only a minimal effort to impeach Lindholm, raising matters unrelated to his testimony implicating Trenkler. Primarily Trenkler’s counsel attempted to challenge Lindholm’s assertion that, as a small boy, he had at one time lived on the same street as Trenkler and to show that Lindholm was at the Plymouth House of Correction in December 1992 in order to provide information to the government on other individuals with whom he had been involved in past criminal activities.
In addition to Lindholm’s testimony, ATF Agents Dennis Leahy and Thomas D’Ambro-sio recounted a November 6, 1991, interview they conducted with Trenkler shortly after the bombing. During this interview, Trenk-ler admitted building the Quincy bomb and sketched a circuit diagram describing it. After making the sketch, Agent D’Ambrosio asked Trenkler how the diagram would differ if Trenkler had used dynamite like that utilized in the Roslindale incident. Both agents testified that, in response to this question, Trenkler drew a second diagram, which featured two sticks of dynamite connected to two electrical blasting caps. Both agents added that they were surprised when they saw the diagram because the use of two electrical blasting caps was a distinctive feature of the Roslindale bomb that, at the time of the interview, had not been disclosed to the public.9 At trial, Leahy also related other conversations he had with Trenkler in which Trenkler conveyed a working knowledge of dynamite and electrical blasting caps.
Leahy further testified about a statement Trenkler made to him at the ATF offices on February 4, 1992. Leahy explained that Trenkler had come to the offices on his own accord to pick up previously-seized business records. Leahy stated that, during his visit, Trenkler engaged Leahy in a long discussion, lasting more than two hours, about the course of the investigation. According to Leahy’s testimony, after Leahy had ended the discussion, Trenkler announced arrogantly upon leaving the ATF offices that “If we did it, then only we know about it. How will you ever find out ... if neither one of us talk[ ]?”
The jury returned a guilty verdict on all counts of the indictment. Subsequently, the district court sentenced Trenkler to concurrent terms of life imprisonment on the counts of receipt of explosive materials and attempted malicious destruction of property by means of explosives and sixty months on the count of conspiracy. Trenkler now appeals.
II.
Discussion
On appeal, Trenkler assigns error to the admission of the Quincy bomb evidence, contending primarily that the incident was not sufficiently similar to the Roslindale bomb to be relevant on the issue of identity, and to the admission of the EXIS database-derived evidence that the government used to prove [52]*52the similarity of the two bombs. Trenkler additionally argues that the district court erroneously admitted several out-of-court statements made by Shay Jr. We discuss each argument in turn.10
A. Quincy Bombing Evidence
We begin with Trenkler’s contention that the district court erred in admitting the evidence of the Quincy bombing.
1. Fed.R.Evid. i04(b): Other Act Evidence
In general, Rule 404(b)11 proscribes the use of other bad-act evidence solely to establish that the defendant has a propensity towards criminal behavior. Rule 404(b)’s proscription, however, is not absolute: the rule permits the use of such evidence if it bears on a material issue such as motive, knowledge or identity. In this Circuit, we have adopted a two-part test for determining the admissibility of Rule 404(b) evidence. E.g., United States v. Williams, 985 F.2d 634, 637 (1st Cir.1993). First, the district court must determine whether the evidence has some “special relevance” independent of its tendency simply to show criminal propensity. E.g., United States v. Guyon, 27 F.3d 723, 728 (1st Cir.1994). Second, if the evidence has “special relevance” on a material issue, the court must then carefully conduct a Rule 40312 analysis to determine if the probative value of the evidence is not substantially outweighed by the danger of unfair prejudice. Williams, 985 F.2d at 637. As with most evidentiary rulings, the district court has considerable leeway in determining whether to admit or exclude Rule 404(b) evidence. Accordingly, we review its decision only under the lens of abuse of discretion. Id.; see also United States v. Fields, 871 F.2d 188, 196 (1st Cir.), cert. denied, 493 U.S. 955, 110 S.Ct. 369, 107 L.Ed.2d 355 (1989).
2. Identity
The government offered the evidence of the Quincy bomb, which Trenkler admitted budding, primarily to prove that Trenkler also built the Roslindale bomb. The government contends that the evidence of the Quincy bomb has “special relevance” on the issue of identity because the numerous similarities surrounding the Quincy and Roslindale incidents compel the conclusion that the same individual built both bombs. Trenkler, on the other hand, argues that the Quincy incident is too dissimilar to be relevant on the issue of identity, and even if it has some relevance, the risk of unfair prejudice that it poses far outweighs its probative value. We agree with the government that the Quincy bomb evidence has “special relevance” on the issue of identity and that the district court did not abuse its considerable discretion in admitting it.
a. Rule k0U(b) Evidence: Special Relevance
When, as in this case, Rule 404(b) evidence is offered because it has “special relevance” on the issue of identity, we have required, as a prerequisite to admission, a showing that there exists a high degree of similarity between the other act and the charged crime. See United States v. [53]*53Ingraham, 832 F.2d 229, 231-33 (1987), cert. denied, 486 U.S. 1009, 108 S.Ct. 1738, 100 L.Ed.2d 202 (1988). Indeed, the proponent must demonstrate that the two acts exhibit a commonality of distinguishing features sufficient to earmark them as the handiwork of the same individual. Id. at 231. This preliminary showing is necessary because
[52]*52Although relevant, evidence may be excluded if its probative value is substantially outweighed by the danger of unfair prejudice, confusion of the issues, or misleading the juiy, or by considerations of undue delay, waste of time, or needless presentation of cumulative evidence.
[53]*53[a] defendant cannot be identified as the perpetrator of the charged act simply because he has at other times committed the same commonplace variety of criminal act except by reference to the forbidden inference of propensity. The question for the court[, therefore, must be] whether the characteristics relied upon are sufficiently idiosyncratic to permit an inference of pattern for purposes of proof.
United States v. Pisari, 636 F.2d 855, 858-59 (1st Cir.1981) (internal quotations and citations omitted) (emphasis added).
Resolving whether the prior act is sufficiently similar to the charged offense to have “special relevance” on the issue of identity, however, is essentially an issue of “preliminary” or “conditional” fact. In other words, the prior act has no tendency to prove the perpetrator’s identity — i.e., it is not relevant — unless the proponent can first establish the conditional fact: that the two acts are sufficiently idiosyncratic to support the inference that they are the handiwork of the same individual. The admissibility of evidence whose relevance turns on the resolution of a conditional fact is governed by Fed.R.Evid. 104(b). See Huddleston v. United States, 485 U.S. 681, 689, 108 S.Ct. 1496, 1501, 99 L.Ed.2d 771 (1988). Rule 104(b) provides, “When the relevancy of evidence depends upon the fulfillment of a condition of fact, the court shall admit it upon, or subject to, the introduction of evidence sufficient to support a finding of the fulfillment of the condition.” Fed.R.Evid. 104(b). Moreover,
[i]n determining whether the Government has introduced sufficient evidence to meet Rule 104(b), the trial court neither weighs credibility nor makes a finding that the Government has proved the conditional fact by a preponderance of the evidence. The court simply examines all the evidence in the case and decides whether the jury could reasonably find the conditional fact ... by a preponderance of the evidence.
Huddleston, 485 U.S. at 690, 108 S.Ct. at 1501. Thus, as here, when a party seeks to admit Rule 404(b) evidence to establish identity, the district court must condition its admission on a showing that the shared characteristics of the other act and the charged offense are sufficiently idiosyncratic that a reasonable jury could find it more likely than not that the same person performed them both.13
[54]*54Trenkler contends that the array of similarities between the two incidents amounts to no more than a collection of “prosaic commonalit[ies that] cannot give rise to an inference that the same person was involved in both acts without reference to propensity.” United States v. Garcia-Rosa, 876 F.2d 209, 225 (1st Cir.1989), cert. denied, 493 U.S. 1030, 110 S.Ct. 742, 107 L.Ed.2d 760, cert. granted and vacated on other grounds sub nom., Rivera-Feliciano v. United States, 498 U.S. 954, 111 S.Ct. 377, 112 L.Ed.2d 391 (1990). However, in resolving whether the evidence supports an inference that the two incidents are “sufficiently idiosyncratic,” we have cautioned that “an exact match is not necessary.” Ingraham, 832 F.2d at 232. The test must focus on the “totality of the comparison,” demanding not a “facsimile or exact replica” but rather the ‘“conjunction of several identifying characteristics or the presence of some highly distinctive quality.’” Id. at 232-33 (quoting Pisari, 636 F.2d at 859) (emphasis added); see also United States v. Myers, 550 F.2d 1036, 1045 (5th Cir.1977) (“[A] number of common features of lesser uniqueness, although insufficient to generate a strong inference of identity if considered separately, may be of significant probative value when considered together.”). In this case, we think the balance of the evidence tilts sufficiently towards admission to satisfy the first step of the Rule 404(b) analysis. Accordingly, we believe that the district court did not abuse its discretion in determining that the numerous similarities in components, design, and technique of assembly, combined with the similar modus operandi and the closeness of geographic proximity between the two events, sufficiently support the inference that the same person built both bombs.
We begin by noting that the government’s explosives expert, Thomas Waskom, testified that his analysis of the similarities shared by the two incidents left him with no doubt “whatsoever” that the same individual built both bombs. Our own review of the record reveals that the two bombs did indeed share a number of similar components and characteristics. Both bombs were remote-controlled, radio-activated, electronic explosive devices. Both were homemade mechanisms, comprising, in general, electronic components easily purchased at a hobby store. Both had similar, though not identical, firing and fusing circuits with separate battery power supplies for each. Both had switches in their fusing circuits to disconnect the radio receivers. To energize their respective radio receivers, both devices utilized similar power supplies, consisting of four AA batteries. Both employed many similar components such as batteries, duct tape, toggle switches, radio receivers, antennas, solder, electrical tape, and large round speaker magnets. Moreover, both used a distinctive method (i.e., twisting, soldering, and taping) to connect some, though not all, of the wires used.14 Though we hardly find any of these factors by themselves to be “highly distinctive,” the coalescence of them is fairly persuasive.15 [55]*55Indeed, even Trenkler’s expert witness, Denny Kline, testified at the pretrial hearing that, in light of these similarities, “there is a possibility, a probability, that maybe there is a connection between the maker of these two bombs.” (Emphasis added.)
Moreover, we note that, in refusing to conclude “beyond a reasonable doubt”16 that the same person built both bombs, Trenkler’s expert Kline eschewed reliance on any factors except the physical evidence. The appropriate test for sufficient similarity, however, is not so limited. “[I]n assessing the sufficiency of the evidence under Rule 104(b), the trial court must consider all evidence presented to the jury.” Huddleston, 485 U.S. at 690-91, 108 S.Ct. at 1502 (emphasis added).
Accordingly, we believe some significance is properly attributed to the simple fact that both incidents are bombings. A bombing, in and of itself, is, arguably, a fairly distinctive method for intimidating or killing an individual. Cf. United States v. Patterson, 20 F.3d 809, 813 (10th Cir.1994) (in a hijacking case, uniqueness of crime itself has significance in Rule 404(b) similarity analysis), cert. denied, — U.S. —, 115 S.Ct. 128, 130 L.Ed.2d 72 (1994); Pisari, 636 F.2d at 858 (“[M]uch more is demanded than the mere repeated commission of crimes of the same class, such as repeated burglaries or thefts. The device used must be so unusual and distinctive as to be like a signature.” (quotations and citations omitted)). In addition, both incidents involved not simply bombs, but remote-control bombs that were placed underneath automotive vehicles.
In both instances, the bombs were constructed and used to benefit a friend of the builder. Trenkler built the Quincy bomb for Donna Shea to use to intimidate the owners of the Capeway Fish Market, and the evidence supported the inference that the person who constructed the Roslindale bomb built it for Shay Jr. to use against his father. Furthermore, in both instances the builder attempted to conceal his or her participation by using a third party to purchase the electronic components used in the explosive device. In 1986, Trenkler initially waited in his car while sending Donna Shea’s nephew into the electronics store with a list to purchase the needed components. Similarly, the evidence supports the inference that the builder of the Roslindale bomb used Shay Jr. to purchase the needed components. Finally, the fact that both bombings occurred within a relatively close geographic proximity must be given some weight in the analysis.
In United States v. Pisari, 636 F.2d 855 (1st Cir.1981), we reversed the district court’s decision to admit evidence of a prior robbery solely on the issue of identity, where the only similarity between it and the charged offense was that a knife was used. Similarly, in Garcia-Rosa, 876 F.2d at 224-25, we refused to sanction the admission of a prior drug transaction where the only characteristic linking it to the charged drug deal was the characteristic exchange of a sample of drugs prior to the sale. In Garcia-Rosa, we held that a single “prosaic commonality” was insufficient “to give rise to an inference that the same person was involved in both acts without reference to propensity.” Id. at 225. See also United States v. Benedetto, 571 F.2d 1246, 1249 (2d Cir.1978) (no signature where shared characteristic is merely “a similar technique for receiving the cash: the passing of folded bills by way of a handshake”).
In the present ease, however, the government presented more than a single “prosaic commonality.” Indeed, the government propounded a laundry list of similarities in design, component selection, construction and overall modus operandi. On the other hand, Trenkler offered a fairly impressive list of differences between the two incidents. In the absence of one or more highly distinctive factors that in themselves point to idiosyn-cracy, we must examine the combination of all the factors. Had Trenkler been unable to point to any significant differences, we suspect he would have had little chance in estab[56]*56lishing an abuse of discretion in allowing the evidence. Similarly, had the government found but three or four common characteristics to establish sufficient similarity, we doubt that the admission of the evidence would have been granted or sustained. Here, in the middle, with substantial evidence on either side and conflicting expert opinions, could a reasonable jury have found it more likely than not that the same person was responsible for both bombs? We think the answer is yes. See Ingraham, 832 F.2d at 233 (admitting evidence) (“[G]iven the host of important comparables, the discrepancies — though themselves not unimportant— go to the weight of the challenged evidence, not to its admissibility.”).17
b. Rule bOJp(b) Evidence: Probative Value and Unfair Prejudice
Resolving that the district court did not abuse its discretion in determining that a rational jury could infer that it was more likely than not that the same person built both bombs, however, does not end the analysis. We must also review the trial court’s determination that the probative value of the evidence was not substantially outweighed by the risk of unfair prejudice. Several factors weigh heavily in this balancing, such as the government’s need for the evidence, see Fields, 871 F.2d at 198 (quoting Fed.R.Evid. 404(b) advisory committee’s note), the strength of evidence establishing the similarity of the two acts, see Huddleston, 485 U.S. at 689 n. 6, 108 S.Ct. at 1501 n. 6, the inflammatory nature of the evidence, and the degree to which it would promote an inference based solely on the defendant’s criminal propensity, see United States v. Rubio-Estrada, 857 F.2d 845, 851-52 (1st Cir.1988) (Torruella, J., dissenting) (explaining inherent unfair prejudice in evidence of prior bad acts).
We believe the district court acted well within its broad discretion in admitting the evidence. First, the evidence was important to the government’s case. The evidence that Trenkler had built the Quincy bomb corroborated David Lindholm’s testimony, identifying Trenkler as the builder of the Roslindale bomb. Second, although the evidence of similarity could have been more compelling, it was nonetheless substantial: Indeed, the government’s explosives expert testified that he had no doubt “whatsoever” that the same person designed and constructed both bombs.
On the other hand, we disagree with the district court that the evidence did not pose any risk of unfair prejudice.18 As with all “bad act” evidence, there is always some danger that the jury will use the evidence not on the narrow point for which it is offered but rather to infer that the defendant has a propensity towards criminal behavior. Nonetheless, outside the context of propensity, the evidence was not unduly inflammatory. The Quincy bomb did not kill or injure any individual and caused little property damage. Moreover, the district court minimized any risk of unfair prejudice by carefully instructing the jury not to use the evidence of the Quincy bombing to infer Trenk-ler’s guilt simply because he was a bad person or because the fact he had a built a bomb in the past made it more likely he had built the bomb in this case. In sum, we believe that the district court did not abuse its discretion in determining that the probative value of the Quincy bomb evidence was not substantially outweighed by the risk of unfair prejudice.19
[57]*57
B. EXIS Database Evidence
Trenkler contends that the district court erred in admitting under the residual hearsay exception, Fed.R.Evid. 803(24),20 testimony about the results of the search of the EXIS database. He maintains that the district court erred because the underlying reports composing the EXIS database lack sufficient guarantees of trustworthiness to fall within the residual hearsay exception. We agree that the district court erred in admitting the evidence, but find the error harmless.
The government offered the EXIS-derived testimony as tending to show that the Roslin-dale and Quincy bombs evinced the signature of a single bomb maker. Specifically, the government offered it as an affirmative assertion that, out of more than 14,000 bombing and attempted bombing incidents, only the Roslindale and the Quincy incidents possessed in common all of the queried characteristics. The district court admitted the EXIS-derived testimony under the residual hearsay exception, finding that it was “sufficiently reliable.” In reaching this conclusion, the court noted that the EXIS database was used and relied upon “by law enforcement authorities on a regular basis.” The government asserts that the district court did not err in admitting the testimony because, in general, the underlying reports were “written objective reports” summarizing careful field and laboratory investigations that the court could permissibly find to be particularly worthy of belief such that “adversarial testing ... would add little to [their] reliability.”
Initially, it is evident that whether or not particular evidence may be admitted under the residual hearsay exception is a fact-specific inquiry committed in the first instance to the sound discretion of the district court. United States v. Doe, 860 F.2d 488, 491 (1st Cir.1988), cert. denied, 490 U.S. 1049 (1989). We accord great deference to the district court’s determination, reviewing it only for an abuse of discretion. E.g., United States v. Benavente Gomez, 921 F.2d 378, 384 (1st Cir.1990). Nevertheless, we will overturn a district court’s determination if, upon careful review, we are left with a “definite and firm conviction that the court made a clear error of judgment” in its decision to admit the testimony. Id. (internal quotations and citations omitted).
Under the residual hearsay exception, the district court must determine, inter alia, whether the proffered evidence possesses “circumstantial guarantees of trustworthi[58]*58ness” equivalent to those possessed by the other listed exceptions to the hearsay rule. See Fed.R.Evid. 803(24); Polansky v. CNA Ins. Co., 852 F.2d 626, 631 (1st Cir.1988); cf. 2 Kenneth S. Broun et al., McCormack on Evidence § 324, at 362 (John W. Strong ed., 4th ed. 1992) (equivalent guarantees of trustworthiness is the most important issue). This trustworthiness inquiry is largely fact driven, and its focus will vary depending on the context in which the issue arises. See Brookover v. Mary Hitchcock Memorial Hosp., 893 F.2d 411, 420 (1st Cir.1990). A court, however, may consider whether the evidence shares reliability factors (e.g., personal knowledge, lack of bias) common to the other hearsay exceptions, see 2 McCormack § 324, at 362-4, and whether the evidence, but for a technicality, would otherwise come within a specific exception, see United States v. Nivica, 887 F.2d 1110, 1126-27 (1st Cir.1989) (where insufficient foundation laid to admit financial documents under business records exception, court had discretion to admit them under residual exception), cert. denied, 494 U.S. 1005 (1990). Essentially, the district court must determine whether the totality of the circumstances surrounding the statement establish its reliability sufficiently enough to justify foregoing the rigors of in-court testimony (e.g., five testimony under oath, cross-examination) that ordinarily guarantee trustworthiness. See Michael H. Graham, Federal Practice and Procedure: Evidence, § 6775, at 737-40 (1992) (courts employ “ad hoc assessment of reliability based upon the totality of the surrounding circumstances”); cf. United States v. Ellis, 935 F.2d 385, 394 (1st Cir.) (citing Idaho v. Wright, 497 U.S. 805, 819, 110 S.Ct. 3139, 3148-49, 111 L.Ed.2d 638 (1990)) (guarantees of trustworthiness in Confrontation Clause context must be established from the “totality of circumstances” surrounding the making of the statement), cert. denied, 502 U.S. 869, 112 S.Ct. 201, 116 L.Ed.2d 160 (1991).
Because we believe that the government clearly failed to establish that the EXIS-derived evidence possessed sufficient “circumstantial guarantees of trustworthiness,” we hold that the district court abused its discretion in admitting the evidence. As noted above, the district court rested its decision to admit the testimony, at least in part, on its finding that law-enforcement agencies use and rely on the database “on a regular basis.” Though we take no issue with this narrow finding, it is hardly dispositive on the issue of trustworthiness. That law enforcement authorities rely on information culled from the database does not, a fortiori, imbue that information with sufficient guarantees of trustworthiness to warrant admission under Rule 803(24). Indeed, law enforcement authorities often rely on information during their investigations (e.g., polygraph examinations, anonymous tips) that would not necessarily be admissible as evidence. See United States v. Scarborough, 43 F.3d 1021, 1026 (6th Cir.1994) (polygraph examinations generally inadmissible); and Fed.R.Evid. 801, 802 (prohibiting hearsay evidence).
More to the point, the government failed to establish that the reports underlying the database possessed any guarantees of trustworthiness similar to those found in the enumerated hearsay exceptions. See generally Fed.R.Evid. 803(1) — (23). Scheid, the government’s expert on EXIS, stated that the database derived from reports submitted by a variety of federal, state and local law enforcement agencies. Though Scheid testified extensively on the reliability of the procedures he followed to cull information from the reports and subsequently input it into the EXIS database, the government offered virtually nothing establishing the reliability of the underlying reports.
On cross-examination, Scheid, who had been solely responsible for EXIS since 1977, admitted that no agency outside of the ATF was required by law to send reports to the EXIS database and that state and local agencies submitting reports were not required to follow any express procedures or conform to any specific standards in collecting or recording the reported information. Indeed, it is far from clear the extent to which information memorialized in any of the reports derives from laboratory analyses, on-the-seene observations of police officers, second-hand descriptions of the device by layperson witnesses, or some other source. Cf. United States v. Scholle, 553 F.2d 1109, 1123-25 (8th [59]*59Cir.) (allowing printouts from Drug Enforcement Administration (“DEA”) computer database where database comprised only chemical analyses performed at regional DEA laboratories), cert. denied, 434 U.S. 940, 98 S.Ct. 432, 54 L.Ed.2d 300 (1977).
Scheid further testified that the submitted reports need not be signed, and that nothing required the author of a submitted report to have personal knowledge of its contents, see Fed.R.Evid. 803 advisory committee’s note (“In a hearsay situation, the declarant is, of course, a witness, and neither this rule nor Rule 804 dispenses with the requirement of firsthand knowledge.”); Fed.R.Evid. 803(6) (business record must be recorded by or from information supplied by an individual with personal knowledge), or for that matter to be qualified as a bomb investigator, see Matthews v. Ashland Chem., Inc., 770 F.2d 1303, 1309-10 (5th Cir.1985); 4 Jack B. Weinstein et al., Weinstein’s Evidence, ¶803(8)[03], at 803-283 (“Questions of the qualification of the expert can be raised as one of the circumstances indicating lack of trustworthiness.”); cf. Beech Aircraft Corp. v. Rainey, 488 U.S. 153, 167 n. 11, 109 S.Ct. 439, 449 n. 11, 102 L.Ed.2d 445 (1988) (“investigator’s skill or experience” is factor establishing trustworthiness of government evaluative report). Finally, Scheid admitted that he employed no procedures for verifying or updating information in the EXIS database that had been submitted by agencies other than ATF.
The underlying reports, arguably, come closest to falling within the hearsay exception for public records and reports, Fed.R.Evid. 803(8). In criminal cases, however, Rule 803(8) does not authorize the prosecution’s use of investigative reports that contain “matters observed by police officers and other law enforcement personnel,” Fed.R.Evid. 803(8)(B), or “factual findings resulting from an investigation made pursuant to an authority granted by law,” Fed.R.Evid. 803(8)(C). See United States v. Arias-Santana, 964 F.2d 1262, 1264 (1st Cir.1992) (police reports offered by prosecution generally inadmissible); but cf, e.g., United States v. Brown, 9 F.3d 907, 911-12 (11th Cir.1993) (Rule 803(8) does not necessarily prohibit the use of police records prepared in a routine non-adversarial setting that do not result from subjective investigation and evaluation), cert. denied, — U.S. —, 115 S.Ct. 152, 130 L.Ed.2d 91 (1994). Moreover, the exception provided by Rule 803(8) is further limited by the general qualification proscribing the use of public records if “the sources of information or other circumstances indicate a lack of trustworthiness.” Fed.R.Evid. 803(8).
We have noted that Congress intended the residual hearsay exception to be used “ ‘very rarely, and only in exceptional circumstances.’” Benavente Gomez, 921 F.2d at 384 (quoting S.Rep. No. 1277, 93d Cong.2d Sess., 20 (1974), reprinted in 1974 U.S.C.C.A.N. 7051, 7066); see also Nivica, 887 F.2d at 1127 (“Rule 803(24) should be used stintingly”). Moreover, Congress did not intend for the exception “ ‘to establish a broad license for trial judges to admit hearsay statements that do not fall within one of the other exceptions’ or ‘to authorize major judicial revisions of the hearsay rule.’ ” Benavente Gomez, 921 F.2d at 384 (quoting S.Rep. No. 1277, 1974 U.S.C.C.A.N. 7066.). In this case, the government failed to establish that the reports composing the EXIS database possessed guarantees of trustworthiness equivalent to the other exceptions to the hearsay rule. Neither are we convinced that the totality of circumstances surrounding the reports adequately assure their reliability where no standardized procedures were employed in creating the reports and the sources of the reported information are unknown. Finally, we find it significant that the government points us to no case in which it has successfully (or unsuccessfully) sought to admit EXIS-derived evidence to prove the identity of a bomb maker. Accordingly, we hold that the district court abused its discretion in admitting the EXIS-derived evidence under the residual exception to the hearsay rule to prove the identity of the builder of the Roslindale bomb.21
[60]*60Although we agree with Trenkler that the district court erred in admitting the EXIS-derived evidence, we nonetheless find the error harmless beyond a reasonable doubt.22 Initially we note that substantial evidence, beyond Trenkler’s participation in the Quincy bombing, supported a finding that he had built the Roslindale bomb. Principally, David Lindholm convincingly testified that, in fact, Trenkler had actually admitted building the Roslindale bomb. Other admissions by Trenkler made to various law enforcement officers inferentially corroborated Lindholm’s testimony, specifically Trenkler’s sketch of the Roslindale bomb, drawn shortly after the explosion and conspicuously featuring two electrical blasting caps. Moreover, Trenkler’s arrogant assertion to Agent Le-ahy that, “if we did it, then only we know about it ... how will you ever find out ... if neither one of us talk[]?” provided further corroboration. Additional support could be inferred from the ample evidence the government adduced establishing Trenkler’s relationship with Shay Jr. and his knowledge of both electronics and explosives.23
Furthermore, the government offered the EXIS-derived evidence to prove that the Roslindale and Quincy bombs were so similar [61]*61that they evinced the signature of a single bomb maker, thus, establishing the relevance of the Quincy bomb evidence on the issue of identity. Our review of the record, however, convinces us that the EXIS-derived evidence was not a critical factor in the district court’s decision to admit the Quincy bomb evidence for the purpose of proving identity. The EXIS-derived evidence was merely cumulative, corroborating the testimony of the government’s explosives expert who, after testifying in detail about the similarities between the two bombs, stated that he had no doubt “whatsoever” that the same person built both bombs.24 Moreover, as discussed supra at 54-56, other circumstantial evidence tending to show that the maker of each bomb used a similar modus operandi {e.g., both bombs built for a friend, both bomb makers used third party to acquire needed components) independently supported the inference that the same person built both bombs. Finally, even putting aside whether the jury would have found the two incidents sufficiently similar to prove identity without the EXIS-de-rived evidence, the jury nonetheless would have been able to consider the fact that Trenkler had designed and built the Quincy bomb to prove Trenkler’s knowledge and skill.
In sum, while the admission of the EXIS-derived evidence would not have been harmless error if the only other evidence consisted of the expert’s testimony of signature and the evidence establishing Trenkler’s relationship with Shay Jr. and his electrical and explosive skills, the additional presence of several different strong sources of testimony relating Trenkler’s admissions, convinces us that no rational jury could have entertained a reasonable doubt of Trenkler’s guilt even in the absence of the EXIS-derived evidence.25
C. Shay Jr.’s Ouir-of-Court Statements
Trenkler additionally asserts that the district court erred by admitting testimony relating ten out-of-court statements purportedly uttered by Shay Jr. The statements, in general, tended to implicate Shay Jr. in the bombing and to suggest that Shay Jr. had not acted alone. The district court admitted the statements either as nonhearsay evidence of Shay Jr.’s state of mind, see Fed.R.Evid. 801(c); 2 McCormack § 269 at 208, or as faffing within the declaration-against-penal-interest exception to the hearsay rule, see Fed.R.Evid. 804(b)(3). Trenkler argues that the admission of these statements violated his rights under the Confrontation Clause.26 We do not agree.
In asserting a Confrontation Clause violation, Trenkler relies primarily on Bruton v. United States, 391 U.S. 123, 88 S.Ct. 1620, 20 L.Ed.2d 476 (1968), in which the Supreme Court held that, in a joint trial, an instruction to the jury to disregard the confession of one non-testifying defendant was insufficient to prevent the confession from unfairly prejudicing the other defendant. Critical to the Bruton Court’s decision was the trial court’s undisputed ruling that the confession was [62]*62inadmissible against the non-confessing defendant. Id. at 128 n. 3, 88 S.Ct. at 1624 n. 3. Bruton has no. application in the present case, however, because the challenged statements here were directly admissible against Trenkler and, consequently, did not pose the Bruton risk of spill-over prejudice. In this case, the district court admitted the statements against Trenkler to establish the existence of the conspiracy.
The Confrontation Clause does not proscribe the use of all out-of-court statements. See Idaho v. Wright, 497 U.S. 805, 813, 110 S.Ct. 3139, 3145, 111 L.Ed.2d 638 (1990). In general, nonhearsay statements or statements not offered to prove the truth of the matter asserted do not raise Confrontation Clause concerns. Tennessee v. Street, 471 U.S. 409, 414, 105 S.Ct. 2078, 2081-82, 85 L.Ed.2d 425 (1985); United States v. Levine, 5 F.3d 1100, 1107 (7th Cir.1993), cert. denied, — U.S. -, 114 S.Ct. 1224, 127 L.Ed.2d 569 (1994). Moreover, the Confrontation Clause does not necessarily prohibit the use of hearsay statements where the trial court has admitted them pursuant to a “firmly-rooted” exception to the hearsay rule or has otherwise found the statements to possess “particularized guarantees of trustworthiness.” See Wright, 497 U.S. at 816, 110 S.Ct. at 3147 (citing Ohio v. Roberts, 448 U.S. 56, 66, 100 S.Ct. 2531, 2539, 65 L.Ed.2d 597 (1980)).
To the extent that the district court admitted the statements as nonhearsay evidence, Trenkler’s Confrontation Clause challenge lacks merit. See Street, 471 U.S. at 414, 105 S.Ct. at 2081-82. As for the rest, we have strongly suggested previously that the exception for declarations against penal interest is a “firmly rooted” exception to the hearsay rule. See United States v. Seeley, 892 F.2d 1, 2 (1st Cir.1989) (“exception for declarations against penal interest would seem to be ‘firmly rooted’ ”). Trenkler does not challenge this assumption, nor does he explain why the statements in question lack “particularized guarantees of trustworthiness.” Accordingly, we are not persuaded . that the district court violated Trenkler’s confrontation rights by admitting them.
III.
Conclusion
For the foregoing reasons, we affirm Trenkler’s conviction.