This is an appeal from the district court’s denial of a petition for a writ of habeas corpus. For the reasons set forth below, we remand the case to the district court.
In the late afternoon of May 29, 1976, the petitioner and Angelo Griffin were at a tavern in Racine, Wisconsin, where they became involved in a dice game with other patrons. When the petitioner refused to pay off on a bet, Griffin pulled the money from the petitioner’s hand. Several minutes later, when the petitioner was standing at approximately the third stool along the bar and Griffin was in front of a cigarette machine at the east end of the bar, the defendant took a gun from his pocket and fired. Griffin threw up his arms and ran toward the defendant, who moved away from the bar. A brief struggle occurred, another shot was fired, and both men fell to the floor. The defendant got up, walked outside, hid the gun, and then returned to the tavern, where he was arrested by police. Griffin, who never moved after falling to the floor, was pronounced dead on arrival at a nearby hospital. An *1290autopsy revealed that Griffin suffered a fatal wound to the chest, which was caused by a bullet that entered the left chest, penetrated the heart and right lung, and lodged beneath the skin of the back. Shortly after the incident, the owner of the tavern discovered a bullet hole in the ceiling of the tavern above the cigarette machine.
An information charging the defendant with first degree murder was filed on July 7, 1976. The defendant’s trial commenced on September 15, 1976, and lasted three days. The state’s theory, as explained during the prosecutors’ opening statement and closing argument, was that the petitioner’s first shot struck Griffin and the second bullet was fired into the ceiling during the ensuing struggle. The prosecutors argued that the petitioner fired the first bullet with the intent to kill, this bullet caused Griffin’s death, and the petitioner therefore committed first degree murder. The defense theory, on the other hand, was that the first bullet did not strike Griffin, but instead lodged harmlessly in the ceiling. According to the defense, Griffin was killed by the second bullet, which the defendant fired during the struggle, when he did not have the criminal intent that is required for a first degree murder conviction.1
A factual dispute relevant to these two theories was whether Griffin would have been capable of engaging in a struggle after receiving his bullet wound. If the wound would have rendered Griffin incapable of such activity, the shot that preceded the struggle could not have caused the wound. The prosecution called as a witness Dr. Myron Schuster, the pathologist who performed the autopsy. Consistent with the state’s “first shot” theory, Dr. Schuster stated that it was possible for Griffin to move under his own power after receiving his wound. Trial Tr. at 230. On cross-examination, Dr. Schuster further testified that it was possible for a person with a bullet wound through the heart and right lung to be capable of strenuous activities for half an hour. Trial Tr. at 232. The defense presented no evidence to refute Dr. Schuster’s testimony. During closing argument, the defense attorney asked the jurors to use their common sense in concluding that Griffin could not have engaged in a struggle after being shot through the heart.
The jury found the petitioner guilty of first degree murder. In a post-conviction motion, the petitioner alleged that he was denied the effective assistance of counsel because his trial counsel failed to reasonably investigate the effect of a heart wound on a person’s ability to maintain physical activity. At a hearing on the motion, which took place on November 11, 1977, the petitioner presented Dr. Billy Bauman, a forensic pathologist, who testified that, in his experience, victims of heart wounds comparable to that of Griffin had been immediately incapacitated upon receiving the wounds. Dr. Bauman expressed his opinion that it would be virtually impossible for victims of such wounds to engage in the physical struggle that was described in the testimony at trial. Furthermore, Dr. Bauman stated that he discussed the nature of Griffin’s wound with six other pathologists, who agreed that the victim of such a wound would “go down ... right away.” Tr. of Proceedings of November 11,1977, at 17-18. The petitioner’s trial counsel also testified at the post-conviction hearing. He said that, after reading Dr. Schuster’s autopsy report prior to trial, he attempted to find a medical opinion to the effect that a bullet wound such as that of Griffin would have caused the immediate collapse of the victim. The trial counsel asserted that this attempt consisted of “discusspng] certain of [Dr. Schuster’s] findings with other physicians,” none of whom were pathologists. Id. at 41. *1291Moreover, the trial counsel testified that, if he had read Dr. Bauman’s report prior to trial, he would have used it to counter Dr. Schuster’s opinion that Griffin was capable of strenuous activity after sustaining his wound.
The trial court denied the petitioner’s post-conviction motion, stating that it did not “think that Doctor Schuster’s testimony was at such great odds with that of Doctor Bauman’s to make a substantial difference in the circumstances” of the case. Id. at 70. The petitioner then appealed his conviction to the Wisconsin Court of Appeals, which rejected his ineffective assistance claim, holding that the trial counsel’s consultation with various physicians was a good faith investigation and did not constitute ineffective assistance of counsel. The petitioner’s subsequent petition for review to the Wisconsin Supreme Court was denied.
On June 9, 1981, the petitioner filed a petition for a writ of habeas corpus with the United States District Court for the Eastern District of Wisconsin. While the petition was pending, the petitioner made a motion to expand the record with an affidavit, in which the petitioner’s trial counsel stated that his pretrial search for a medical opinion consisted of speaking to one radiologist, who had no-expertise or training in either cardiology or traumatic injuries to the heart. The petitioner also moved for an evidentiary hearing on the ground that material facts were not adequately developed at the state court hearing. The district court denied the petitioner’s motion for an evidentiary hearing, finding that, after the post-conviction hearing that took place in state court, “another hearing on the same issue in [the federal district] court would be of no benefit____” Rogers v. Israel, No. 81-C-653, unpublished decision and order at 4 (E.D.Wis. Nov. 22, 1982). With regard to the ineffective assistance claim, the district court considered the performance of the petitioner’s trial counsel during the trial, as well as the trial counsel’s testimony during the post-conviction hearing,2 and it concluded that the representation received by the petitioner met minimum standards of professional competence. After reviewing both Dr. Bauman’s oral testimony at the post-conviction hearing and his written report, which had been entered into evidence at the hearing, the district court concluded that, in light of the evidence supporting the state’s “first shot” theory, “Dr. Bauman’s testimony was not as persuasive as [the petitioner] asserts.” Id. at 6. The court thus denied the petition for a writ of habeas corpus.
In appealing this ruling, the petitioner argues that, contrary to the district court’s conclusion, Dr. Bauman’s testimony could have made a difference in the jury verdict. However, on the issue of whether the trial counsel’s pretrial search for such testimony was reasonably competent, the petitioner asserts that a remand is necessary because the facts surrounding this search were not developed adequately at the post-conviction hearing. The petitioner further argues that, if this court finds a remand unnecessary, the conviction should nonetheless be reversed because it was unreasonable for the trial counsel to fail to consult an expert when investigating the effects of the victim’s heart wound. The state responds, first, that the absence of Dr. Bauman’s testimony at trial did not affect the verdict because this testimony was not very different from Dr. Schuster’s testimony and also because other overwhelming evidence supports the defendant’s conviction beyond a reasonable doubt. Second, on the issue of the adequacy of the trial counsel’s search for expert testimony, the state asserts that a remand to develop the facts is improper and that the factual record developed at the post-conviction hearing fails to prove that the trial counsel’s search was unreasonable.
I. STANDARD FOR ASSESSING EFFECTIVE ASSISTANCE OF COUNSEL
When determining whether a defendant received ineffective assistance of *1292counsel in violation of the sixth amendment, “[t]he benchmark ... must be whether counsel’s conduct so undermined the proper functioning of the adversarial process that the trial cannot be relied on as having produced a just result.” Strickland v. Washington, — U.S. -, 104 S.Ct. 2052, 2064, 80 L.Ed.2d 674 (1984). Accordingly, the Supreme Court has ruled that the defendant must show both that the defense counsel’s performance was deficient and that the deficient performance prejudiced the defense. Id. We shall consider these two prongs in reverse order.3
A. Prejudice to Defense
To establish that a defense counsel’s performance prejudiced the defense, “[a] defendant must show that there is a reasonable probability that, but for counsel’s unprofessional errors, the result of the proceeding would have been different.” Id. 104 S.Ct. at 2068. Thus, where a defendant challenges his conviction, “the question is whether there is a reasonable probability that, absent the error, the fact-finder would have had a reasonable doubt respecting guilt.” Id. 104 S.Ct. at 2069. As defined by the Supreme Court, “reasonable probability” is “a probability sufficient to undermine confidence in the outcome.” Id. 104 S.Ct. at 2068.
In deciding whether a defense counsel’s failure to investigate expert opinions was prejudicial, courts have considered whether such opinions were critical to the presentation of a defense. See United States v. Fessel, 531 F.2d 1275 (5th Cir.1976) (where evidence that defendant committed offense was virtually uncontested and only issue was sanity of defendant at time of offense, failure of counsel to move for court-appointed psychiatrist under 18 U.S.C. § 3006A(e) constituted ineffective assistance of counsel). See also United States v. Baynes, 687 F.2d 659 (3d Cir.1982) (where only evidence against defendant was intercepted tape recording, failure of defense counsel to investigate possibility of distinguishing exemplar of defendant’s voice from voice on intercepted tape was prejudicial to defense). In addition, when determining prejudice, courts have taken into account both the defense counsel’s success in eliciting favorable expert testimony through the cross-examination of government witnesses, see Hall v. Sumner, 682 F.2d 786, 789 (9th Cir.1982), and the overall strength of the prosecution’s case, see Solomon v. Kemp, 735 F.2d 395, 402 (11th Cir.1984).
Under the facts of the present case, there was no question that the petitioner fired a bullet that killed Griffin. The only issue was whether it was the first or second bullet. A review of the record indicates that the eyewitness testimony and the physical evidence presented at trial supported both the “first shot” theory of the state and the “second shot” theory of the defense.
Most of the eyewitnesses testified that the petitioner fired the first shot at Griffin while holding the gun with his arm extended parallel to the floor, a description that supports the state’s theory that the first shot struck Griffin. However, one eyewitness stated that the petitioner held the gun at an upward angle of 45°, a description that agrees with the testimony of a private investigator, who examined the bullet hole in the ceiling and concluded that the missed shot originated from a spot between the third and fourth stools along the bar and entered the ceiling at a 45° angle.4 The *1293investigator’s conclusion clearly supports the defense theory that the petitioner fired the first bullet into the ceiling while standing at approximately the third stool along the bar.
At trial, the state presented a ballistics expert, who testified that powder burns on the clothes surrounding Griffin’s wound revealed that Griffin was shot from a distance of four feet, and that burns on Griffin’s right forehead indicated that a shot missed him from a closer distance. This testimony coincided with the state’s theory that Griffin was struck by the first shot, when the petitioner and Griffin were between two and eight feet apart, and that the petitioner fired into the ceiling during the struggle, when the two men were closer together. However, as pointed out by the defense counsel during closing argument, the petitioner was facing Griffin in such a way that an errant first shot would have passed Griffin’s right forehead. Moreover, there was testimony that, during the struggle, the petitioner was backing away from Griffin, and the two men were within arm’s contact of each other, but not “hugging.” Trial Tr. at 137. Thus, the powder burns on Griffin’s clothes are consistent with the defense theory that the second shot struck Griffin from a distance of several feet while Griffin was coming toward the petitioner and while the two were struggling within arm’s reach.
The eyewitnesses testified at trial that Griffin threw up his arms after the first shot, and one witness demonstrated that Griffin grabbed his chest, thus supporting the “first shot” theory. Yet, all the witnesses also testified that after the first shot, Griffin moved under his own power toward the petitioner and a struggle ensued for a period between thirty seconds and two minutes, during which time Griffin and the petitioner moved north of the bar. This description supports the defense theory that the ceiling shot, which originated from the direction of the bar, had been the first shot. Furthermore, all witnesses agreed that Griffin fell to the floor immediately after the second shot was fired, and Griffin’s blood was found only on the spot where he fell, lending further support to the defense’s “second shot” theory.
As the foregoing evidence demonstrates, it is a close question as to which bullet struck Griffin. The state contended at oral argument that the case is not difficult at all when we take into account the petitioner’s testimony that he intended to hit Griffin with his first shot. We disagree. The parties stipulated at trial that, shortly after the shooting, the petitioner’s blood alcohol level was measured at .27, Trial Tr. at 225, which was interpreted by Dr. Schuster as intoxication, Trial Tr. at 236-37. In addition, the eyewitnesses testified that the petitioner pulled the gun from his pocket very quickly, and the petitioner asserted that he did not take time to aim. Considering this evidence and the physical evidence discussed earlier, the fact that the petitioner intended to hit Griffin with the first shot is not dispositive proof that he succeeded.
In light of the record before us, we disagree with the district court’s assessment that the state’s case was strong, and we conclude that expert testimony regarding Griffin’s ability to engage in physical activity after sustaining a severe heart wound was critical to the presentation of the defense. We also find that the Wisconsin trial court’s conclusion that the testimony of Dr. Schuster did not differ significantly from that of Dr. Bauman is not fairly supported by the record. Dr. Schuster testified on direct examination that it was possible for Griffin to move under his own power after sustaining his wound. Rather than weakening this opinion during cross-examination, Dr. Schuster responded to the defense counsel’s cross-examination questions by stating that half an hour of physical activity was possible after the receipt of such a wound. Dr. Bauman, on the other *1294hand, testified at the post-eonviction hearing that Griffin’s wound would “cause immediate incapacitation,” and that it was “virtually impossible” for Griffin to have maintained physical activity after being shot. Tr. of Proceedings of November 11, 1977, at 15-16. Although. Dr. Bauman understandably hesitated to phrase his opinion in unconditional terms, the fact remains that Dr. Bauman unequivocally testified that, in his experience, he had never seen a case where the victim of a serious heart wound did not collapse immediately.
We thus hold that under the very close facts of this case, there is a reasonable probability that if expert testimony such as that of Dr. Bauman had been presented at trial, the jury would have had a reasonable doubt respecting guilt on the charge of first degree murder.
B. Adequacy of Defense Counsel’s Performance
Under the second prong of the Strickland test, a defendant must show that the defense counsel’s representation fell below an objective standard of reasonableness. Strickland v. Washington, 104 S.Ct. at 2065. Although this standard is reflected in guides such as the American Bar Association Standards for Criminal Justice 4-1.1 to 4-8.6 (2d ed. 1980), the proper measure of attorney performance in each case is “simply reasonableness under prevailing professional norms,” considering all the circumstances from the defense counsel’s perspective at the time. Id. When measuring a defense counsel’s performance against this standard, “a court must indulge a strong presumption that counsel’s conduct falls within the wide range of reasonable professional assistance” that might be considered sound trial strategy. Id. 104 S.Ct. at 2065-66. See also United States v. Payne, 741 F.2d 887, 891 (7th Cir.1984); United States v. Weston, 708 F.2d 302, 306 (7th Cir.), cert. denied, — U.S. -, 104 S.Ct. 397, 78 L.Ed.2d 340 (1983).
Thus, while it is undisputed that a defense counsel should make reasonable inquiry into all defenses, see Arrowood v. Clusen, 732 F.2d 1364, 1370 (7th Cir.1984), “a particular decision not to investigate must be directly assessed for reasonableness in all the circumstances, applying a heavy measure of deference to counsel’s judgment.” Strickland v. Washington, 104 S.Ct. at 2066. In several cases, the failure to investigate and present expert testimony has been found to be a matter of trial tactics within the range of reasonableperformance. See United States v. Krohn, 560 F.2d 293, 297 (7th Cir.) (failure of defense counsel to call fingerprint expert), cert. denied, 434 U.S. 895, 98 S.Ct. 275, 54 L.Ed.2d 182 (1977); Hall v. Sumner, 512 F.Supp. 1014 (N.D.Cal.1981) (failure of defense counsel to present expert testimony on effects of particular level of blood alcohol), aff'd, 682 F.2d 786 (9th Cir. 1982). Yet, under certain circumstances, “it may be vital in affording effective representation to a defendant in a criminal case for counsel to elicit expert testimony rebutting the state’s expert testimony.” Knott v. Mabry, 671 F.2d 1208, 1212-13 (8th Cir.), cert. denied, 459 U.S. 851, 103 S.Ct. 115, 74 L.Ed.2d 101 (1982). Cf. Williams v. Martin, 618 F.2d 1021, 1027 (4th Cir.1980) (where substantial question requiring expert testimony arose over the cause of victim’s death, trial judge’s refusal to provide expert deprived defendant of effective assistance of counsel).
The amount of investigation into expert opinions that may be required of a defense attorney is discussed in Davis v. Alabama, 596 F.2d 1214, 1221 (5th Cir.1979), vacated as moot, 446 U.S. 903, 100 S.Ct. 1827, 64 L.Ed.2d 256 (1980). In Davis, the defense counsel made no effort to investigate or develop possible sources of evidence regarding the defendant’s sanity, even though the counsel knew that the defendant had a history of mental problems and that insanity was the only possible defense. The Fifth Circuit noted that, under Alabama law, even a general practitioner could have testified regarding a defendant’s sanity, and it observed that the defense counsel made no effort to have the defendant examined by a physician or to establish facts on which a physician could have based an *1295opinion on the defendant’s sanity. The court ruled that, by failing to investigate, the defense counsel did not discharge the duty that they owed to their client, and the court remanded the case for an evidentiary hearing to determine whether the defense counsel would have uncovered helpful evidence if they had acted properly.
In the present case, at least seven pathologists in the Racine area held the opinion that a bullet wound such as that suffered by Griffin would cause the immediate collapse of the victim. Although we decline to rule that the defense counsel was required to contact a pathologist, we hold, as the court in Davis similarly held, that the defense counsel owed a duty to the petitioner to ask a qualified expert whether Griffin would have been immediately incapacitated by his wound. We find that, under the particular factual circumstances of this case as known to the defense counsel at the time of trial, the failure to make such an inquiry would have been unreasonable5 and could not have been based on sound trial strategy.6
II. NEED FOR EVIDENTIARY HEARING
It is settled, under Wisconsin law regarding expert witnesses, that “if a person has qualifications in a field, he may testify within the area of his competency---- It is the particular qualifications of the witness in relation to the particular issue which should control rather than the label of a profession or trade.” Roberts v. State, 41 Wis.2d 537, 551, 164 N.W.2d 525, 531-32 (1969). See also Karl v. Employers Insurance of Wausau, 78 Wis.2d 284, 297, 254 N.W.2d 255, 261 (1977). In the present case, it has never been determined whether the “physicians” consulted by the defense counsel could have been qualified as medical experts on the subject of the physical capacity of a victim who suffers a bullet wound to the heart, and facts necessary to this determination were not explored at the post-conviction hearing.
Where material facts were not adequately developed at the state court hearing, the petitioner is entitled, under both 28 U.S.C. § 2254(d) (1982) and Townsend v. Sain, 372 U.S. 293, 83 S.Ct. 745, 9 L.Ed.2d 770 (1963), to an evidentiary hearing in federal district court, provided that the failure to develop the state court record was not due to inexcusable neglect or deliberate bypass.7 See Thomas v. Zant, 697 F.2d 977, 983-86 (11th Cir.1983). See gen*1296erally United States ex rel. Jones v. Franzen, 676 F.2d 261, 268-70 (7th Cir.1982) (Posner, J., concurring). Thus, in order to obtain this federal hearing, a defendant must show the district court that the undeveloped facts were material and that there was no inexcusable neglect or deliberate bypass in failing to develop these facts. Thomas v. Zant, 697 F.2d at 988. In the present case, it is evident that material facts regarding the experience of the consulted physicians were not developed at the state court hearing, and absent inexcusable neglect or deliberate bypass, the district court erred in denying the petitioner’s motion for an evidentiary hearing.
Accordingly, we remand this case to the district court, where the petitioner must show that the failure to develop facts regarding the consulted physicians was not due to inexcusable neglect or deliberate bypass. If the petitioner fails in this showing, the writ of habeas corpus will be denied.8 If the petitioner succeeds in showing the absence of inexcusable neglect or deliberate bypass, the district court must hold an evidentiary hearing, at which both parties may present evidence regarding the defense counsel’s efforts to obtain expert testimony. If, after this hearing, the district court finds that none of the physicians consulted by the defense counsel could have been qualified as an expert, the counsel’s performance must be judged to have been unreasonable and prejudicial, as discussed in this opinion, and the writ will be granted. If, on the other hand, the district court finds that the trial counsel consulted a physician who could have been qualified as an expert, thereby fulfilling his duty toward his client, the writ will be denied.
. Thus, during closing argument, the defense attorney argued that the jury could find the petitioner guilty either of no offense, if it found that he fired the second bullet out of self defense, or of a lesser included offense, if it found that he fired the second bullet out of an unreasonable fear of harm.
The state has never contended that the jury could have convicted the petitioner of first degree murder if it found that the second bullet killed Griffin.
. The district court did not consider the information in the trial counsel’s affidavit, thus implicitly denying the petitioner’s motion to expand the record.
. The court in Strickland stated that, although it had discussed the performance component of ineffectiveness prior to the prejudice component, "there is no reason for a court deciding an ineffective assistance claim to approach the inquiry in the same order or even to address both components of the inquiry if the defendant makes an insufficient showing on one.” Strickland v. Washington, — U.S. -, 104 S.Ct. 2052, 2069, 80 L.Ed.2d 674 (1984).
. The private investigator explained that he placed a swizzle stick through the bullet hole in the ceiling tile and observed that the stick pointed at a 45° angle in a southwesternly direction toward a spot between the third and fourth stools along the bar. Trial Tr. at 361-62.
The strength of this evidence is illustrated by the trial court’s response to the petitioner’s post-trial motion for review of the jury verdict. The court suggested that, in light of the investigator’s *1293testimony regarding the bullet hole, the jury could have concluded that the second bullet hit the ceiling during the struggle if it found that “somehow this bullet ricocheted from another object ... [even though] [t]here was no proof of any mark from which it may have ricocheted ____” Trial Tr. at 510.
. The fact that the trial counsel’s performance was otherwise admirable would not excuse the failure to conduct a proper investigation. See Moore v. United States, 432 F.2d 730, 739 (3d Cir.1970) (en banc) (“representation involves more than the courtroom conduct of the advocate. The exercise of the utmost skill during the trial is not enough if counsel has neglected the necessary investigation and preparation of the case ... ”).
. Indeed, at the post-conviction hearing, the trial counsel indicated that, as part of his trial strategy, he had hoped to obtain favorable expert testimony, and he would have presented testimony like that of Dr. Bauman if he had found it.
. The Court in Townsend stated that
[i]f for any reason not attributable to the inexcusable neglect of the petitioner, see Fay v. Noia, 372 U.S., p. 438 [83 S.Ct., p. 848] evidence critical to the adequate consideration of the constitutional claim was not developed at the state hearing, a federal hearing is compelled. The standard of inexcusable default set down in Fay v. Noia adequately protects the legitimate state interest in orderly criminal procedure____
Townsend v. Sain, 372 U.S. 293, 317, 83 S.Ct. 745, 759, 9 L.Ed.2d 770 (1963). In Fay, the Court held that “the federal habeas judge may in his discretion deny relief to an applicant who has deliberately bypassed the orderly procedure of the state courts and in so doing had forfeited his state court remedies.” Fay v. Noia, 372 U.S. 391, 438, 83 S.Ct. 822, 848, 9 L.Ed.2d 837 (1963).
The Eighth Circuit, in Guice v. Fortenberry, 661 F.2d 496 (5th Cir.1981) (en banc), applied the inexcusable neglect/deliberate bypass standard where facts crucial to a habeas petition were not developed at the state court hearing. The court noted that there was "no substantial allegation that the petitioners made a tactical choice to leave the evidence undeveloped." Id. at 507. Observing that it appeared that at the state court hearing, "the defendants and their attorneys did not appreciate fully the relevance of the missing evidence,” the court held that such neglect is not inexcusable within the mean*1296ing of Townsend and Fay. Id. See Wright & Sofaer, Federal Habeas Corpus for State Prisoners: The Allocation of Fact-Finding Responsibility, 75 Yale L.J. 895, 971 & n. 273 (1966) ("where counsel ... failed because of insufficient preparation or other neglect to marshall all crucial evidence underlying a federal claim, a knowing default should not be found____ [Townsend ] reflects [the] position that unintentional flaws of counsel should not bar the assertion or full development of federal rights”). See abo Thomas v. Zant, 697 F.2d 977, 981 n. 6 (11th Cir. 1983).
. Without showing the absence of inexcusable neglect or deliberate bypass, the petitioner is considered to have waived further development of facts. See generally Fay v. Noia, 372 U.S. at 438, 83 S.Ct. at 848; Thomas v. Zant, 697 F.2d at 981. In the present case, the facts that were established at the state court hearing do not demonstrate that the "physicians” consulted by the trial counsel could not have been qualified as experts. Thus, if we were to consider only these facts, we could not conclude that the petitioner met his burden of demonstrating ineffective assistance of counsel. See, e.g., Marino v. United States, 600 F.2d 462, 464 (5th Cir.1979) (“a defendant represented by retained counsel who urges ineffectiveness of counsel bears the burden of establishing that charge, by a preponderance of the evidence”).