GOLDBERG, Circuit Judge:
No one denies that James Davis, the appellant in this case, killed his wife. He pleaded not guilty by reason of insanity— his only possible defense — but a jury in Cullman County, Alabama, convicted him of first degree murder. After unsuccessfully pursuing his state remedies he petitioned for federal habeas corpus. He alleged that there were a number of constitutional errors in his trial. The United States District Court for the Northern District of Alabama dismissed his petition. When Davis appealed, we upheld the district court on several grounds but remanded for an evidentiary hearing to determine if Davis had received the effective assistance of counsel. Davis v. Alabama, 545 F.2d 460, 467 (5th Cir.), cert. denied, 431 U.S. 957, 97 S.Ct. 2682, 53 L.Ed.2d 275 (1977). On remand a hearing was held before a magistrate, who recommended that Davis be given a new trial. The district judge disagreed and ruled against Davis. Davis appeals again. We reverse because we believe that Davis’s trial attorneys failed to discharge their duty to their client. We remand for a further hearing on the question of whether their failure prejudiced Davis.
Approximately two months before his trial, two attorneys were appointed to represent Davis. On the day of the trial, they moved for a continuance. They said they needed time to develop an insanity defense. They cited their “heavy caseload” and the duties one of the attorneys had in the legislature. R. Vol. 1 at 73. Since Davis lived in California and was only visiting in Alabama at the time of the crime, see R. Vol. 2 at 27, 62-63, they wanted more time “mainly for the purpose of getting information from the State of California on this question of insanity.” R. Vol. 1 at 74. To support their motion for continuance, they adduced only one piece of evidence — the report of a psychologist named Dr. Dean who had recently treated Davis in California. They acknowledged, however, that they had known of Dr. Dean’s treatments for several weeks, R. Vol. 1 at 68-69, 70— 71,1 and in addition the report principally discussed Davis’s alcoholism. The trial judge denied the motion for a continuance and the ease immediately proceeded to trial.
At trial Davis’s attorneys put on only the shell of an insanity defense. In Alabama, a variety of evidence can be used to prove insanity; the testimony of lay witnesses [1216]*1216and general medical practitioners, as well as that of experts, is admissible. See e. g., Hamilton v. State, 281 Ala. 448, 203 So.2d 684, 686-87 (1967); Smith v. State, 263 Ala. 1. 82 So.2d 296 (1955). And while the record is unclear, it suggests that a considerable amount of evidence might have been used in support of Davis’s insanity plea.2 But Davis’s trial attorneys called exactly one witness — the sheriff who arrested him. He testified that Davis often seemed “quite —fairly strange.” The defense attorneys called no other lay witnesses. They called no medical witnesses, even though general practitioners, at least, were readily available in the area. See R. Vol. 1 at 83-84, 326.3 All of this is undisputed, and it requires us to suspect at once that Davis has not received anything approaching the effective assistance of competent counsel. See Hintz v. Beto, 379 F.2d 937 (5th Cir. 1967). See also Greer v. Beto, 379 F.2d 923, 925 (5th Cir. 1967); McCollum v. Bush, 344 F.2d 672 (5th Cir. 1965).
Indeed, even Davis’s trial lawyers agreed that their representation of Davis was ineffective. They blamed the trial judge’s refusal to grant a continuance for their deficient performance. But when we examine the denial of a continuance we must focus on “the reasons presented to the trial judge at the time the request is denied,” Ungar v. Sarafite, 376 U.S. 575, 589, 84 S.Ct. 841, 850,11 L.Ed.2d 921 (1964); see United States v. Uptain, 531 F.2d 1281, 1285-86 (5th Cir. 1976); McKinney v. Wainwright, 488 F.2d 28, 29-30 (5th Cir.), cert. denied, 416 U.S. 973, 94 S.Ct. 1998, 40 L.Ed.2d 562 (1974), and recognize that the question is traditionally within the discretion of the trial judge, see Ungar v. Sarafite, 84 S.Ct. at 850; Avery v. Alabama, 308 U.S. 444, 60 S.Ct. 321, 322, 84 L.Ed. 377 (1940). Davis’s defense attorneys’ motion for a continuance was so unsupported by explanation or evidence that the trial judge cannot be faulted for denying it. When they made the motion and again at the evidentiary hearing on Davis’s federal habeas petition, the defense attorneys acknowledged that they had known of Davis’s mental problems from the start. See p. 1218 & n. 8 infra. Nevertheless, they gave the trial judge virtually no explanation for their failure to “get [] information from . California” sooner.4 They asked the trial judge to appoint a doctor and to allow him time to examine Davis, but they did not explain why they had failed to make that request, or to find a doctor themselves,5 during the several weeks they were [1217]*1217involved with the case. See R. Vol. 1 at 68, 83, 70.
Instead of blaming the judge we hold that Davis’s trial attorneys were responsible for the inadequacy of Davis’s defense.6 We have often said that a defense attorney must be prepared to investigate and develop evidence on behalf of his client. “It is the duty of the lawyer to conduct a prompt investigation of the circumstances of the case and explore all avenues leading to facts relevant to guilt and to a degree of guilt or penalty.” American Bar Association Project on Standards for Criminal Justice, Standards Relating to the Prosecution Function and the Defense Function § 4.1 (tent, draft 1970). An attorney does not provide effective assistance if he fails to investigate sources of evidence which may be helpful to the defense. See, e. g., Rummel v. Estelle, 590 F.2d 103,104-05 (5th Cir. 1979); Gaines v. Hopper, 575 F.2d 1147 (5th Cir. 1978); Bell v. Georgia, 554 F.2d 1360, 1361 (5th Cir. 1977); Gomez v. Beto, 462 F.2d 596 (5th Cir. 1972); Chalk v. Beto, 429 F.2d 225, 227 (5th Cir. 1970); King v. Beto, 429 F.2d 221, 224 (5th Cir. 1970), cert. denied, 401 U.S. 936, 91 S.Ct. 921, 28 L.Ed.2d 216 (1971); Caraway v. Beto, 421 F.2d 636, 637-38 (5th Cir. 1970).
Davis’s attorneys made practically no efforts to develop such information. This is undisputed. Davis had relatives in California who might have known, firsthand or secondhand, about his background of mental problems; but as the magistrate found, “[i]t is apparent that . . . defense counsel made no effort prior to the time of [1218]*1218trial to secure the testimony of lay persons in California who had had an opportunity to observe irrational acts [by] Davis.” R. Vol. 1 at 326. The attorneys might have telephoned California. They might have written to one of Davis’s relatives there.7 There is no evidence that they did anything of the sort. Similarly, we would have thought it axiomatic that defense attorneys considering an insanity defense should have their client examined by a psychiatrist or psychologist. In Alabama, as we have said, see pp. 1215-1216 supra, even a general practitioner can testify to the defendant’s insanity. As the magistrate found: “Any local physician could have been called to testify as to his sanity. Yet the record strongly implies that no effort was made prior to trial to have Davis examined by a physician or to establish facts on which a physician could have based an opinion of Davis’ sanity.” R. Vol. 1 at 326.
Moreover, it was utterly clear from the start that an effective defense required some investigation. Davis’s attorneys knew almost from the time they first met Davis that he was mentally unstable and had a history of mental problems. The district court suggested, see R. Vol. 1 at 337-38, that except for Dr. Dean’s report the defense attorneys had no evidence indicating that Davis was insane; this suggestion is contradicted by the defense attorneys themselves. At the habeas hearing one of them acknowledged that Dr. Dean’s report was “the main thing” but testified:
Q. [D]id you have . . . anything other than this one encounter with Dr. Dean in California?
A. “Yes. We had all kinds of information about him, about problems he had had when he was a kid on up. As a matter of fact, we wanted to go to other cases where he had convictions and where he had been in court before because of problems he had had from it while he was a small kid. As I recall, one where he and his brother took money from the offering plate at a church, for example
R. Vol. 2 at 55-56. This defense attorney— appointed two months before the trial — also testified:
We had known for a month or two that there was some insanity in his background or some problems where he had to see a psychiatrist.
R. Vol. 2 at 46. When they argued for a continuance the defense attorneys cited the facts of the crime itself as evidence of Davis’s insanity. R. Vol. 1 at 74. They repeatedly said that their own encounters with Davis convinced them that he had mental problems.8
Not only did the defense attorneys know that insanity was a possible defense; they apparently knew that it was Davis’s only possible defense. Thus their failure to investigate cannot be excused by saying that it did not seem to be a very strong defense. In deciding not to develop the insanity defense Davis’s attorneys effectively decided to put on no defense at all. We cannot say that such an approach amounts to adequate representation. See Bell v. Georgia, 554 F.2d 1360, 1361 (5th Cir. 1977); Gomez v. Beto, 462 F.2d 596, 597 (5th Cir. 1972).
In addition, Davis’s attorneys knew that he lived in California and had grown up [1219]*1219there, so that evidence of his background would likely be found there; they also knew, of course, of the role of medical testimony in an insanity defense, see R. Vol. 1 at 83. And they knew — or thought they knew9 — that Davis himself would not be able to assist them very much in preparing the defense. Davis’s trial counsel, discussing his request for a continuance, testified at the habeas hearing: “. . .1 was of the opinion that we could gain some additional information if we were allowed to go out there and take depositions. Because just to tell you the truth, Mr. Davis didn’t seem competent to me to tell us a lot about himself and his case.” R. Vol. 2 at 47. He also testified:
THE COURT: Did [Davis] appear to be able to remember events in his life and to relate those events to you?
A. Your Honor, this is one of the problems that he appeared to have. He just didn’t seem to be able to recall a lot of things that had happened in the past.
R. Vol. 2 at 60, and:
THE COURT: Other than his experience with . . . Dr. Dean . . . did he tell you of any other incident in his past?
A. He couldn’t remember a lot about them. He had been in and out of trouble so much, he couldn’t really remember. I think the major scrapes he had had with the law, he remembered back .
But he didn’t recall all the facts about that.
R. Vol. 2 at 60.
In summary, Davis’s attorneys knew that Davis had a history of mental problems, knew that insanity was his only possible defense, knew, or thought, that Davis himself would be little help in developing the defense, knew what possible outside sources might be developed, and — to judge from what they said when they argued for a continuance — knew that without some investigation they had practically no defense to offer. Still they made no effort to investigate or develop the possible sources of evidence. This is not a borderline case; it is a clear breach of the duty a defense attorney owes to his client.
Accordingly, the state’s effort to exonerate Davis’s attorneys by saying that Davis might have given them more leads, more evidence of his insanity, is mostly irrelevant. Davis’s attorneys had a clear duty to investigate and did not fulfill it. That failure is not somehow offset just because Davis himself might have made the defense less of a sham by volunteering information. But the state’s suggestion raises larger and more interesting issues. The state and the district court seemed to believe that by not informing his attorneys of all the evidence of insanity he knew, Davis somehow failed in his duty to his attorneys.10 But eliciting relevant information from the client is a central part of the defense attorney’s task. Long ago, for example, the Fourth Circuit held ineffective a defense attorney whose failure to explain a possible defense to his client resulted in the client’s not disclosing information which would have established the defense. See Coles v. Peyton, 389 F.2d 224, 226-27 (4th Cir.), cert. denied 393 U.S. 849, 89 S.Ct. 80, 21 L.Ed.2d 120 (1968). In other words, a defendant’s failure to disclose certain information to his attorney is not necessarily, or obviously, or even probably the defendant’s fault. We must examine the facts of each case. Even defenses which seem straightforward to lawyers may be misunderstood by defendants or may be beyond their com[1220]*1220prehension.11 Legal insanity, Davis’s defense, is an unusually difficult and technical notion, and a defendant cannot be expected to know what facts are relevant to it. For example, Davis told his attorneys about Dr. Dean, who had treated him until he left for his visit to Alabama, but Davis may not have realized that earlier events and treatments were also relevant. We should not hold a defendant responsible for failing to reveal certain information to his attorney unless the attorney has made every reasonable effort to elicit the information, has made his client aware of the sort of information that might be relevant, and has given his client an opportunity to disclose it. We do not know that Davis’s attorneys did any of those things.12
When a defendant has mental problems, as Davis evidently did, it is even more unrealistic to penalize him for failing to disclose every relevant piece of information to his attorneys. As we have said, see p. 1218 & n. 8 supra, Davis’s apparent mental condition caused his attorneys not to take him seriously as a source of evidence; under those circumstances, it is difficult for us to blame Davis for the information that did not come to light. An attorney who does seriously interview an arguably insane client may find him to be one of those many insane persons who placidly insist that they are entirely sane; and the attorney is likely to find that an arguably insane client is not the best or most reliable source of information. The state suggests that because Davis was found competent to stand trial, he is to be blamed for not disclosing evidence to his attorneys. But not only must we take account of the fact that Davis’s attorneys apparently did not interview him very intensively; more generally, a finding that a defendant is competent does not entitle his counsel to act as if the defendant were intelligent, articulate, and learned in the law. An attorney must take account of his client’s particular incapacities and weaknesses, and a reviewing court must examine the specific dealings between them.13
For these reasons we have no difficulty holding that Davis’s attorneys, by failing to develop and investigate possible sources of evidence, did not discharge their duty to their client. In saying this we do not suggest that Davis’s attorneys were generally inept; perhaps they thought that when they told the trial judge of their work load they would be given more time. Perhaps [1221]*1221that is the reason they did not try to develop the insanity defense before trial. Perhaps they would have succeeded with another trial judge, but this judge, trying his first case, see R. Vol. 1 at 15, insisted on more evidence of insanity and denied the continuance. Perhaps it was all simply a miscalculation. But the defense of this indigent, possibly insane accused did not call for a calculation balancing his rights against the attorneys’ convenience. It did not call for brinkmanship with the defendant’s only possible defense. It called for thoughtful, thorough preparation and investigation. Instead it received virtually none.
Nevertheless we cannot yet order that Davis be given a new trial, because we do not know that his attorneys would have uncovered evidence helpful to his defense even if they had acted properly. The record does suggest, fairly strongly, that some such evidence exists. For example, (1) a clinical psychologist who has examined Davis since his trial reported his “strong latent aggressive feeling” toward women, his “paranoid thinking,” and his “schizo-affective disorder,” R. Vol. at 36; (2) Davis was discharged from the Army for failing to adjust to military life, see R. Vol. 2 at 21, 70, which may suggest psychological problems; (3) after Davis’s conviction, and apparently at the request of the attorney who handled his habeas corpus petition, Davis’s mother wrote a letter describing some of his irrational behavior. R. Vol. 2 at 11 — 12; R. Vol. 1 at 325.14 But this evidence has not been critically examined or connected to Davis’s condition at the time of the crime.15 Therefore we remand to the district court for another hearing devoted solely to the question of whether Davis’s attorneys’ misfeasance prejudiced him. At this hearing Davis will bear the burden of proof,16 but he need only show that his attorneys’ errors were not “harmless beyond a reasonable doubt,” see Chapman v. California, 386 U.S. 18, 24, 87 S.Ct. 824, 17 L.Ed.2d 705 (1967). If he makes such a showing, he will be entitled to a new trial on the ground that he has not received the “reasonably effective assistance” of counsel. MacKenna v. Ellis, 280 F.2d 592, 599 (5th Cir. 1960), cert. denied, 368 U.S. 877, 82 S.Ct. 121, 7 L.Ed.2d 78 (1961).
We are dealing with a crucially important right, so our holding on this point is narrow. Not every defendant whose attorney was deficient must show prejudice. The Supreme Court has said that “[t]he right to have the assistance of counsel is too fundamental and absolute to allow courts to indulge in nice calculations as to the amount of prejudice resulting from its denial,” Glasser v. United States, 315 U.S. 60, 76, 62 S.Ct. 457, 467, 86 L.Ed. 680 (1942), and has held that the denial of counsel at a critical stage of a criminal proceeding is always considered prejudicial. See, e. g., Chapman v. California, 386 U.S. 18, 23 & n. 8, 87 S.Ct. 824, 17 L.Ed.2d 705 (1967); White v. Maryland, 373 U.S. 59, 60, 83 S.Ct. 1050, 10 L.Ed.2d 193 (1963). “That, indeed, was the whole point of Gideon v. Wainwright, 372 U.S. 335, [83 S.Ct. 792, 9 L.Ed.2d 799] [1963].” Chapman v. California, 386 U.S. at 43, 87 S.Ct. at 837 (Stewart, J., concurring). But “the purpose of Gideon was not merely to supply criminal defendants with warm bodies, but rather to guarantee reasonably competent representation,” Cooper v. Fitzharris, 551 F.2d 1162, 1164 (9th Cir. 1977), so if a defense attorney were to put on what amounted to no de[1222]*1222fense at all, we would “not stop to determine whether prejudice resulted,” Hamilton v. Alabama, 368 U.S. 52, 55, 82 S.Ct. 157, 159, 7 L.Ed.2d 114 (1961).
The Supreme Court has gone further than this, however; indeed the Court seems never to have applied the harmless error doctrine to a case involving the ineffective assistance of counsel. But see Brooks v. Tennessee, 406 U.S. 605, 92 S.Ct. 1891, 1895, 32 L.Ed.2d 358 (1972). In three recent cases involving ineffective representation the Court pointedly found constitutional violations without inquiring into prejudice. In Geders v. United States, 425 U.S. 80, 96 S.Ct. 1330, 47 L.Ed.2d 592 (1976), rev’g. United States v. Fink, 502 F.2d 1 (5th Cir. 1974), the trial court prohibited a defendant from consulting his attorney during an overnight recess that separated the defendant’s direct testimony from cross-examination. Because the defendant had shown no prejudice, we held that he had not been denied the effective assistance of counsel, see 502 F.2d at 9; the Supreme Court, requiring no showing of prejudice, reversed. In Herring v. New York, 422 U.S. 853, 95 S.Ct. 2550, 45 L.Ed.2d 593 (1975), the Supreme Court held that refusing to allow defense counsel to make a closing argument at trial violated the defendant’s right to the effective assistance of counsel, even if the issues were simple and the prosecution's case very strong. See id. 95 S.Ct. at 2556, 2553. Finally, in Holloway v. Arkansas, 435 U.S. 475, 98 S.Ct. 1173, 55 L.Ed.2d 426 (1978), the Court held that whenever a trial court improperly permits or requires the same attorney to represent two defendants at a joint trial, “reversal is automatic” even if neither defendant can show specifically that he was prejudiced. Id. 98 S.Ct. at 1180-82.
Some circuits have gone further still and have held that a defendant never needs to show prejudice in order to establish that he has been denied the effective assistance of counsel. See Cooper v. Fitzharris, 551 F.2d 1162, 1164-65 (9th Cir. 1977); Beasley v. United States, 491 F.2d 687, 696-97 (6th Cir. 1974); but see United States v. Sumlin, 567 F.2d 684, 688 (6th Cir. 1977), cert. denied, 434 U.S. 932 (1978). Other circuits disagree and explicitly require a prejudice to be shown in some cases. See United States v. Cooper, 580 F.2d-259, 263 n. 8 (7th Cir. 1978); McQueen v. Swenson, 498 F.2d 207, 218-20 (8th Cir. 1973); United States ex rel. Green v. Rundle, 434 F.2d 1112, 1115-16 (3rd Cir. 1970); United States v. DeCoster, 159 U.S.App.D.C. 326, 333, 487 F.2d 1197, 1204 (1973) (placing burden on government to show lack of prejudice); Coles v. Peyton, 389 F.2d 224, 226 (4th Cir.), cert. denied 393 U.S. 849, 89 S.Ct. 80, 21 L.Ed.2d 120 (1968) (same). See also United States v. Bosch, 584 F.2d 1113,1123 (1st Cir. 1978) (leaving question open).
We have sometimes intimated that a defense attorney’s shortcomings vitiate a conviction only if they prejudice the defendant. See Friedman v. United States, 588 F.2d 1010, 1016, 1017 (5th Cir. 1979); Thomas v. Estelle, 588 F.2d 170, 171 (5th Cir. 1979); Buckelew v. United States, 575 F.2d 515, 521 (5th Cir. 1978); Pennington v. Beto, 437 F.2d 1281, 1285 (5th Cir. 1971). See also Sand v. Estelle, 551 F.2d 49 (5th Cir. 1977), cert. denied, 434 U.S. 1076, 98 S.Ct. 1267, 55 L.Ed.2d 783 (1978); Cheely v. United States, 535 F.2d 934, 936 (5th Cir. 1976). All of these cases involved an attorney’s failure to conduct an adequate investigation of possible defenses, and we believe this is decisive. Not every variety of attorney ineffectiveness should be treated in the same way. If an attorney has not adequately investigated possible defenses, it will often, although not always, be appropriate to ask whether a defendant was prejudiced before ordering a new trial.
We reach this conclusion for several reasons. First, a court deciding whether a failure to investigate was prejudicial ordinarily will perform a task to which it is suited. Usually it need only examine the specific evidence that an investigation would have uncovered; it will determine how prospective witnesses will testify and whether certain tangible evidence exists. Affidavits, depositions, or if necessary live testimony will generally be reliable and economical means of deciding the question. [1223]*1223By contrast, a court will face a far less congenial prospect if it attempts to decide whether prejudice has resulted from, for example, the kind of ineffectiveness involved in Holloway, where an attorney was forced to represent defendants with conflicting interests. Such a court would have to examine the various strategies that the attorney might have pursued and the choices the defendants might have made had they all not been hamstrung by the attorney’s conflict; as the Supreme Court noted, this task will often be difficult or “virtually impossible” and would require “unguided speculation,” see Holloway v. Arkansas, 435 U.S. 475, 98 S.Ct. 1173, 1181-82 (1978). Similarly, a court would not be well equipped to inquire into the prejudice caused by an attorney’s failure to consult sufficiently with his client — a failure which was mandated by the trial judge in Geders but might also result from the attorney’s dereliction. A court could intelligently evaluate prejudice in such a case only by becoming closely familiar with both the course of the trial and the relationship between the attorney and the client; then the court would have to put itself in the place of an attorney who was better informed by a client who was better advised, and decide what different decisions that attorney would have made. This will often be a hopelessly intricate task, especially compared to the accumulation of relatively concrete evidence which will be the sole function of the district court on remand here. For this reason, our holding does not conflict with Holloway or Geders; nor does it require that prejudice be shown before an attorney is held ineffective for representing clients with differing interests or for failing to consult adequately with his client.
Relatedly, a court examining the prejudice caused by an attorney’s failure to investigate can, for the most part, avoid speculating about how a jury would have reacted to certain evidence or certain events at trial. See Sand v. Estelle, 551 F.2d 49, 51 (5th Cir. 1977), cert. denied, 434 U.S. 1076, 98 S.Ct. 1267 (1978). To be sure, the court will have to decide whether it is satisfied, beyond a reasonable doubt, that the jury’s verdict would not have been altered by the evidence presented to it. But this is a threshold inquiry into whether evidence is sufficient to create a question for the jury; it is the sort of inquiry that courts must often make. See generally Chapman v. California, 386 U.S. 18, 24, 87 S.Ct. 824, 17 L.Ed.2d 705 (1967). Indeed it is not unlike the question a federal trial judge answers when he decides whether the defendant has adduced enough evidence of insanity to warrant submitting the issue to the jury. See Davis v. United States, 160 U.S. 469, 476, 16 S.Ct. 353, 40 L.Ed. 499 (1895). By contrast, inquiring into the prejudice resulting from other alleged forms of attorney ineffectiveness will often demand a much more thoroughgoing replication of the jury’s function. Thus in Herring v. New York the Supreme Court recognized how difficult it is to imagine not just the summation an attorney would have given, had he been allowed, but the reaction that the finder of fact would have had. See 422 U.S. 853, 95 S.Ct. 2550, 2555-56 & n. 15 (1975). The same may sometimes be true of a variety of trial decisions — for example, a decision not to prepare or call a certain witness, not to cross-examine a witness, or not to object to certain evidence, see e. g., Cooper v. Fitzharris, 551 F.2d 1162 (9th Cir. 1977) — that reflect deficient performance by an attorney. So those cases, too, like Herring, are comfortably distinguishable from the situation we address here. Of course, the facts of each case must be examined; in each case we must assess the advisability of requiring a showing of prejudice. Sometimes, it may be inappropriate to insist that a defendant show prejudice when his attorney has failed to investigate his case adequately; sometimes it will be appropriate to require a defendant to show how he was injured by some other variety of attorney dereliction.
Because we hold that Davis’s trial attorneys did not discharge their duty to their client, we reverse the judgment of the district court. The case is remanded for a hearing on the single question of whether the attorneys’ conduct prejudiced Davis. If it did, Davis is entitled to a new trial.
REVERSED and REMANDED.