United States Court of Appeals For the First Circuit
No. 25-1090
UNITED STATES,
Appellee,
v.
DIEGO FERNÁNDEZ-SANTOS,
Defendant, Appellant.
APPEAL FROM THE UNITED STATES DISTRICT COURT FOR THE DISTRICT OF PUERTO RICO
[Hon. Francisco A. Besosa, U.S. District Judge]
Before
Gelpí, Thompson, and Rikelman, Circuit Judges.
Samuel P. Carrion, Assistant Federal Public Defender, with whom Rachel Brill, Federal Public Defender, District of Puerto Rico, Franco L. Pérez-Redondo, Assistant Federal Public Defender, Supervisor, Appellate Division, and Kevin E. Lerman, Assistant Federal Public Defender, were on brief, for appellant. Maarja T. Luhtaru, Assistant United States Attorney, with whom W. Stephen Muldrow, United States Attorney, and Juan Carlos Reyes-Ramos, Assistant United States Attorney, Chief, Appellate Division, were on brief, for appellee.
May 15, 2026 RIKELMAN, Circuit Judge. Diego Fernández-Santos
("Fernández") appeals his sentence for violating the terms of his
supervised release. He argues that the government failed to prove
the critical fact that drove his sentence, leading the district
court to commit a procedural error by looking outside the
revocation record to justify the sentence. We agree with Fernández
that a procedural error occurred and thus vacate and remand for
resentencing.
I. BACKGROUND
In 2014, Fernández pleaded guilty to multiple federal
criminal charges, including possession of a firearm (a compact
pistol) by a prohibited person. See 18 U.S.C. § 922(g)(1). The
district court sentenced him to over six years in prison for these
crimes, followed by three years of supervised release.
In February 2023, after Fernández completed his prison
sentence but while he was still on supervised release, he was
arrested again. At the time of his arrest, the police seized a
rifle and ammunition from a bedroom closet in the house where
Fernández was living, as well as a pistol and a gun magazine from
a bag that an officer testified he saw Fernández discard outside
the house. The officers did not see Fernández near the rifle nor
is there any evidence in the record that he had ever handled it.
Fernández's probation officer promptly notified the
district court of the arrest and alleged that Fernández had
- 2 - violated several conditions of his supervised release. One of
those conditions prohibited Fernández from "possess[ing] a
firearm, ammunition, destructive device, or any other dangerous
weapon." After Fernández waived his preliminary revocation
hearing, a magistrate judge found probable cause for the alleged
violations and referred the case to the district court for a final
revocation hearing.
Meanwhile, the government charged Fernández with new
criminal conduct based on the arrest -- possession of a firearm by
a prohibited person and possession of a machine gun. See 18 U.S.C.
§ 922(g)(1), (o).1 As part of his defense against these new
criminal charges, Fernández moved to suppress the evidence seized
at his arrest. The district court granted his motion in part: It
ordered the suppression of the pistol, and other items found in
the discarded bag, but not the rifle the police found in a bedroom
of the house.
The trial on the new firearm charges against Fernández
began in December 2024. At the trial, the government introduced
an "expert in the identification of machine guns," Homeland
Security Investigations Agent Ariel Pérez-Nieves ("Pérez"). Agent
Pérez testified that the rifle seized during Fernández's arrest
1The initial indictment only charged Fernández with a violation of § 922(g)(1), but in May 2024, a grand jury returned a superseding indictment that also included the § 922(o) charge.
- 3 - was an "AK-47 style" rifle that functioned as a machine gun,
meaning that someone operating the gun could fire multiple rounds
with one pull of the trigger. He also explained that the gun had
a visible "lever" and three small, unmarked dash lines. According
to Agent Pérez, the lever and dash lines indicated that the gun
had three possible settings: safety, automatic, and semiautomatic.
He pointed out, however, that the rifle would not function as a
machine gun unless an automatic sear was installed inside it and
a sear pin held that sear in place. He also testified that the
sear pin was small but visible, that he could not identify one of
the other pins in the rifle, and that all the pins looked
"similar." Finally, Agent Pérez explained that the only way he
was able to conclude with certainty that the firearm was a machine
gun was by firing it.
Five days into the trial, the district court dismissed
the new firearm charges against Fernández with prejudice due to
discovery violations by the government. With these new charges
wiped away, the court scheduled Fernández's final revocation
hearing to determine whether he had violated the terms of his
supervised release for his 2014 convictions.
In advance of the final revocation hearing, the
government filed an Informative Motion with the district court.
It contended that Fernández had committed a Grade A violation of
his supervised release terms by possessing a "destructive
- 4 - device" -- a machine gun -- despite his prior felony conviction.
See U.S. Sent'g Guidelines Manual ("U.S.S.G.")
§ 7B1.1(a)(1)(A)(iii) (U.S. Sent'g Comm'n 2024) (defining a
Grade A violation as "a federal, state, or local offense punishable
by a term of imprisonment exceeding one year that . . . involves
possession of a . . . destructive device," such as a machine gun).
It then requested that the court impose the statutory maximum
sentence of 60 months.
The government submitted six exhibits, which it attached
to the Informative Motion, as evidence of the violations. The
exhibits contained excerpts of witness testimony from the
suppression hearing and the jury trial on the dismissed § 922(g)(1)
and § 922(o) charges against Fernández. The government even
highlighted portions of the testimony that it viewed as critical.
Exhibit Six is particularly important. That exhibit
consisted of excerpts from the trial testimony of two government
experts: Alcohol Tobacco and Firearms Agent Jorge Escribano, an
expert in the "identification of firearms," and Agent Pérez. The
government included four pages of trial testimony by Agent
Escribano. In that testimony, he identified the firearm that was
seized during Fernández's arrest as "an AK-type rifle" that
"qualif[ies] as a firearm under [f]ederal law" and was "not
manufactured in the Commonwealth of Puerto Rico." The government
- 5 - included only one page of trial testimony by Agent Pérez. That
testimony reads:
Q: Special Agent P[é]rez, showing you Government's Exhibit 22, what is that?
A: It is a rifle, an AK-47 style.
Q: Have you seen that rifle before?
A: Yes, sir.
Q: How do you know?
A: Ah, this rifle was inspected, examined by me. It has the engraving that we did the testing on it.
Q: What was your conclusion once you tested it?
A: It was found to be a -- to operate as a machine gun.
Beyond the exhibits attached to the Informative Motion,
the government did not introduce any other evidence to support its
allegations that Fernández had violated the terms of his supervised
release. It even expressly stated to the district court that it
was "resting [its] case on the transcripts" attached to that
motion. It also reiterated -- "[j]ust so the record is
clear" -- that it had "highlight[ed] excerpts from those
transcripts that support [the] allegations" against Fernández.
For his part, Fernández emphasized that it was the
government's burden to prove by a preponderance of the evidence
each of the supervised release violations that it had alleged, as
- 6 - well as the grade of those violations. Although Fernández did not
contest some of the alleged violations, he vigorously disputed
that he knowingly possessed a machine gun. He went on to argue
that the government had failed to prove this violation, explaining
that the evidence it had submitted with its Informative Motion did
not establish that he possessed the "AK-47 style" rifle at all,
much less "prove [his] knowledge of the components of that weapon
as a machine[ ]gun."
The district court ultimately found that Fernández had
engaged in conduct that violated several of his supervised release
conditions, including (as relevant here) possessing a rifle. So
the court revoked his supervision term. And after "tak[ing] into
consideration" the arguments and evidence introduced by the
government and Fernández, "including those parts of the
Suppression Hearing and the trial, which they mentioned today,"
the court then found that Fernández "knew that the rifle was a
machine[ ]gun" -- meaning that he had committed a Grade A
violation. The court also provided its basis for this finding: The
firearm "had a visible switch to set the rifle on safety, on
semiautomatic firing mode, and on automatic firing mode." This
"obvious" "switch" -- combined with Fernández's "familiar[ity]
with weapons" given his prior firearm conviction for possession of
a compact pistol -- was enough, in the court's view, to find by a
preponderance of the evidence that Fernández knowingly possessed
- 7 - a machine gun. The court proceeded to sentence Fernández to the
statutory maximum of 60 months in prison followed by another year
of supervised release.
Fernández promptly objected to the procedural and
substantive reasonableness of the sentence. In particular, he
maintained that the "Government [did] not prove[] Grade A
violations" because it did "not prove[] knowledge or mens rea for
the characteristics of the machine[ ]gun." The district court
overruled his objections.
Fernández timely appealed.
II. STANDARD OF REVIEW
Because Fernández preserved his arguments as to whether
he knowingly possessed a machine gun, we review his challenge to
his sentence for abuse of discretion. See United States v.
Colón-Maldonado, 953 F.3d 1, 3 (1st Cir. 2020) (quoting United
States v. Wright, 812 F.3d 27, 30 (1st Cir. 2016)).
Generally, our review of sentencing errors involves a
well-established two-step framework. See United States v.
Colón-Cordero, 91 F.4th 41, 48 (1st Cir. 2024). "[W]e first
determine whether the sentence imposed is procedurally reasonable
and then," if needed, evaluate "whether it is substantively
reasonable." Id. (quoting United States v. Clogston, 662 F.3d
588, 590 (1st Cir. 2011)).
- 8 - III. DISCUSSION
Fernández lodges several challenges to his revocation
sentence. We begin and end our analysis with his contention that
a procedural error occurred because the district court relied on
extra-record evidence to find that he knowingly possessed a machine
gun, and that finding then drove his sentence.
According to Fernández, the limited evidence that the
government introduced during the revocation proceeding did not
support a finding that he knowingly possessed a machine gun. In
response, the government defends the district court's finding that
the visible switch was enough to put Fernández on notice that the
rifle was a machine gun, and it does so by citing to extra-record
evidence. But as Fernández points out, the district court could
not rely on extra-record evidence in imposing his revocation
sentence without violating his due process rights and the
requirements of Federal Rule of Criminal Procedure 32.1(b)(2). We
agree with Fernández.
If an individual commits a new crime while on supervised
release, a district court may revoke the supervised release term
and impose a new sentence. See Colón-Maldonado, 953 F.3d at 3.
"To guide the sentencing decision, the United States Sentencing
Guidelines set three grades of supervised release
violations . . . ." Id. The highest, Grade A, applies to conduct
including the "possession of a firearm or destructive device of a
- 9 - type described in 26 U.S.C. § 5845(a)," such as a machine gun.
U.S.S.G. § 7B1.1(a)(1)(A)(iii). As with all supervised release
violations, "the government must prove [a Grade A violation] by a
preponderance of the evidence." Colón-Maldonado, 953 F.3d at 3.
Although revocations of "'supervised release are not
considered part of a criminal prosecution, they nevertheless
entail a loss of freedom and a deprivation of liberty,'" and thus
raise "the same due process and fairness considerations." United
States v. Ramos-Carreras, 59 F.4th 1, 6 (1st Cir. 2023) (quoting
United States v. Correa-Torres, 326 F.3d 18, 22 (1st Cir. 2003)).
As a result, individuals like Fernández who face supervised release
revocation proceedings are "entitled to a panoply of procedural
rights." Correa-Torres, 326 F.3d at 22. Those rights include
"the right to be sentenced on the basis of accurate and reliable
information" and "the opportunity to rebut the . . . evidence and
the information." Ramos-Carreras, 59 F.4th at 5 (quoting United
States v. Rivera-Rodríguez, 489 F.3d 48, 53 (1st Cir. 2007)); see
also Fed. R. Crim. P. 32.1(b)(2) (outlining procedural
requirements for final revocation hearing).2
2We recently held that "Rule 32.1(b)(2)(C)'s limited confrontation right applies to the entirety of the revocation proceeding, both in the determination of whether the releasee has violated the conditions of supervised release and in the determination of whether to revoke supervised release and impose a term of imprisonment." United States v. García-Oquendo, 144 F.4th 66, 76 (1st Cir. 2025).
- 10 - To be sure, "[a] district court has broad discretion at
sentencing to consider information pertaining to the defendant and
the defendant's offense conduct." Ramos-Carreras, 59 F.4th at 5
(quoting United States v. Millán-Isaac, 749 F.3d 57, 69 (1st Cir.
2014)). But, as we just discussed, this discretion is "bounded by
both Federal Rule of Criminal Procedure 32 and the demands of due
process." United States v. Bramley, 847 F.3d 1, 5 (1st Cir. 2017).
For that reason, we have held that a "district court's [material]
use of new information" from outside the sentencing record "in
determining a sentence[] can be reversible error."
Ramos-Carreras, 59 F.4th at 5 (citing Rivera-Rodríguez, 489 F.3d
at 54).
To cut to the chase, the government had the burden to
establish that Fernández knowingly possessed a machine gun (as we
will explain later). But for reasons that remain unclear, the
government chose not to include in the revocation record most of
the expert testimony about the rifle's characteristics that it
introduced during the trial on the new charges, which were
ultimately dismissed.
Tellingly, the portions of the trial transcript that the
government cites on appeal to bolster the district court's finding
were not attached to its Informative Motion. As Fernández
describes, he crafted his litigation strategy during the
revocation proceeding based on the evidence the government
- 11 - submitted, given that the burden of proof always remained on the
government. Had he known that the government, or the district
court, would rely on other evidence, he could have crafted a
different strategy. Defense attorneys, he intimates, have no
reason to rebut evidence that the government never bothered to
introduce.
In response, the government makes two arguments. First,
it contends that it did not need to establish that Fernández
knowingly possessed a machine gun. Instead, it only needed to
show that he possessed a machine gun because, in its view, the
Sentencing Guidelines do not impose a mens rea requirement.
Second, it claims that, even if it did need to show mens rea, the
district court could rely on all the trial testimony (which was
not new to Fernández) either via judicial notice or because that
evidence was incorporated into the revocation proceeding. On the
record here, we cannot agree with the government on either point.
The government has waived its first argument. In its
appeal brief, the government contends that the text of the
Sentencing Guidelines does not contain a mens rea requirement for
Grade A violations. See U.S.S.G. § 7B1.1(a)(1) (defining Grade A
supervised release violations as "conduct constituting" certain
offenses punishable by imprisonment exceeding one year, including
an offense that "involves possession" of a machine gun). But the
government never raised this argument to the district court.
- 12 - Instead, it litigated this case on the premise that it was
obligated to prove that Fernández knowingly possessed a machine
gun. And, because the government did not raise this argument, the
district court did not decide whether the Sentencing Guidelines
impose such a requirement, and Fernández was only able to respond
to this argument in his appellate reply brief.
As our precedent makes clear, we rarely consider
arguments not raised before the district court. See Shabshelowitz
v. State of R.I. Dep't. of Pub. Safety, 155 F.4th 62, 66 (1st Cir.
2025) ("If any principle is settled in this circuit, it is
that . . . legal theories not raised squarely in the lower court
cannot be broached for the first time on appeal." (citation
omitted)). Of course, we can affirm on alternative grounds, as
the government correctly points out. But we generally do so only
when we can rely on well-established legal principles or when those
alternative grounds are readily "manifest in the record." Brox v.
Woods Hole, 83 F.4th 87, 98 (1st Cir. 2023). Here, however, the
government is asking us to affirm by resolving a complex legal
question about the correct interpretation of the Sentencing
Guidelines that we have not addressed before, even though that
issue was not litigated by the parties below and the district court
did not have the opportunity to rule on it.
"Appellate courts are, by definition, courts of review,"
not of "first instance," and it would be imprudent to resolve legal
- 13 - issues without full adversarial briefing or the benefit of a
district court ruling. O'Brien v. United States, 56 F.4th 139,
151 (1st Cir. 2022); see United States v. Lorenzo-Hernandez, 279
F.3d 19, 22 (1st Cir. 2002) (declining to consider the government's
new legal argument on appeal when "the government did not present
this argument to the district court"); see also United States v.
Carrasco-De-Jesus, 589 F.3d 22, 26 & 26 n.1 (1st Cir. 2009)
(applying the waiver doctrine against the government because "what
is sauce for a defendant's goose is most often sauce for the
government's gander"). Thus, we decline to overlook the
government's waiver here.
Turning to the government's second argument, we cannot
agree that, despite the limited evidence the government submitted
to support the revocation allegations, the district court could
rely on all the trial testimony related to the dismissed charges
without any notice to Fernández. Importantly, the government does
not dispute that the court based its mens rea finding on the
"obvious" "switch" on the firearm, combined with Fernández's
previous conviction for possession of a pistol. According to the
government, that finding was supported by "the trial testimony of
Agent Pérez, who explained the characteristics of the gun and the
switch."
But the testimony the government highlights on appeal to
support the district court's finding is nowhere in the revocation
- 14 - record. The government emphasizes that the district court's
language at the revocation hearing "closely track[ed] Agent
Pérez's trial testimony," including that "the rifle had a lever"
to change the firing mode to automatic. As support, it cites six
pages of Agent Pérez's trial testimony (pages 43-45 and 50-52).
Yet the government put only one page of Agent Pérez's trial
testimony into the revocation record (page 43). And as our
quotation of that one page of testimony demonstrates, it included
no mention of a switch or lever or its significance (as opposed to
the other features of the firearm) in determining the functioning
of the rifle. See supra at 6. Indeed, the government concedes
that the revocation record lacks any testimony about the rifle's
switch or lever. And, in any event, the entirety of Agent Pérez's
testimony, including his cross examination, is more nuanced than
the six pages of direct-examination testimony that the government
cites in its brief.
The government attempts to overcome its failure to put
evidence into the revocation record, suggesting to us during oral
argument that the district court could have taken judicial notice
of all the trial testimony on the dismissed charges or that this
testimony was incorporated into the revocation record. Cf. United
States v. Rivera-Ruperto, 852 F.3d 1, 15 n.16 (1st Cir. 2017)
(noting that "absent exceptional circumstances, we generally
consider as waived issues raised only at oral argument"). But the
- 15 - government never asked the district court to take judicial notice
of this testimony or incorporate it into the record. Instead, the
government did the opposite; it reiterated that to prove the
alleged violations it was resting entirely on the exhibits it
attached to its Informative Motion.
Had the government tried to introduce during the
revocation proceeding the evidence it now cites on appeal,
Fernández would have had the opportunity to object, to introduce
contrary evidence or, at a minimum, to develop an argument
challenging the force of the government's evidence. Against that
full adversarial record, we then could have reviewed any factual
findings by the district court for clear error. Instead, Fernández
built his revocation defense around the evidence that the
government submitted in its Informative Motion. He made the
understandable strategic decision not to dispute evidence that was
not in that record.
Ultimately, it was the government's litigation strategy
during the revocation proceeding that led the district court to
rely on extra-record evidence. We cannot, as the government urges
us to do, simply ignore its failure to introduce that evidence
into the revocation record, which it easily could have done. A
district court cannot rely on such extra-record evidence without
treading on a defendant's due process rights. See, e.g.,
- 16 - Millán-Isaac, 749 F.3d at 73 (remanding when the district court
relied on extra-record evidence at the sentencing hearing).
Especially when the government seeks to take away an
individual's liberty, it "must turn square corners." Ferrara v.
United States, 456 F.3d 278, 280 (1st Cir. 2006); see Dep't of
Homeland Sec. v. Regents of the Univ. of Cal., 591 U.S. 1, 24
(2020) (reviewing agency decision to rescind immigration program
and noting that, "when so much is at stake, . . . the Government
should turn square corners in dealing with the people" (citation
modified)). The government did not do so here.3
IV. CONCLUSION
For all these reasons, we vacate Fernández's sentence
and remand for resentencing consistent with this opinion, limited
3 Because we vacate Fernández's sentence based on this procedural error, we do not reach his other challenges, which include an argument based on the recent ruling in United States v. Esteras, 606 U.S. 185 (2025). See, e.g., Millán-Isaac, 749 F.3d at 73 n.9 (reasoning that decision to vacate and remand for resentencing due to procedural error made it unnecessary to reach the defendant's remaining challenges). We note, however, that on remand the district court will have the benefit of Esteras, which the Supreme Court handed down after the revocation hearing. See 606 U.S. at 188 (discussing the relevant 18 U.S.C. § 3553(a) factors in the supervised release context).
- 17 - to the current revocation record.4 See Ramos-Carreras, 59 F.4th
at 8 n.6.
4 Fernández asks us to remand to a different district court judge. But we remand to a new judge "only in very unusual cases." United States v. Nieves-Díaz, 173 F.4th 8, 16 (1st Cir. 2026) (quoting United States v. Vázquez-Méndez, 915 F.3d 85, 88 (1st Cir. 2019)). And having reviewed Fernández's request, we see no reason to do so in this case, especially given that it was the government's mistake that set the stage for the error here. See United States v. Castillo-Torres, 8 F.4th 68, 73 (1st Cir. 2021); cf. United States v. Rosa-Borges, Nos. 24-1841, 24-1842, 2026 WL 1194736, at *6 (1st Cir. May 1, 2026) (remanding to a different judge for resentencing after the district court, unprompted by the government, relied on information outside the record, without citing any source for that information or providing notice to the defendant that it would consider such information).
- 18 -