I join in the majority opinion affirming defendant’s conviction of two counts of first degree murder, and upholding the jury’s finding of the multiple-murder special circumstance. But because of trial counsel’s constitutionally inadequate representation of defendant at the penalty phase of this capital case, I do not join in the majority’s denial of defendant’s petition for writ of habeas corpus, insofar as that petition challenges the adequacy of trial counsel’s performance at the penalty phase.
The record of the thorough evidentiary hearing, ably conducted by a superior court judge sitting as this court’s habeas corpus referee, demonstrates a total failure by trial counsel to adequately investigate, prepare, and *210present defendant’s case at the penalty phase. Incredibly, in this capital case, counsel spent a total of only 40 hours preparing for both the guilt and penalty phases of the trial. Counsel’s trial file contained no notes or legal research, and his only substantive interview with defendant took place at the courthouse on the morning of the start of trial. With respect to the penalty phase, counsel conducted virtually no investigation, and he made no effort to present mitigating evidence through witnesses whom he could have called. As the referee dryly commented at the evidentiary hearing, “when it comes down to somebody’s life being at stake, attorneys should at least call some witnesses, make some effort.” Had counsel done so, the jury would have heard from defendant’s many family members who were prepared to testify about his character and background, and the jury would have heard from experts who could have explained that, at the time of the crimes, defendant’s insulin-dependent diabetes and use of phencyclidine (PCP) may have significantly affected his behavior. Counsel’s failure to present this evidence undermines confidence in the judgment of death, requiring that the death sentence be reversed and a new penalty trial conducted.
I.
On the morning of February 3, 1983, defendant, who was then 21 years old, left the house of his friend, Patricia Harper, and entered a nearby residence, where he shot and killed Ora Mae Pope and Edward Moreno. Defendant was charged with capital murder. At the guilt phase of the trial, defense counsel’s entire presentation on defendant’s behalf consisted of playing the audio tape-recording of defendant’s statements to the police and making a closing argument.1 Similarly minimal were counsel’s efforts at the penalty phase. There he made no opening statement, called only one defense witness, and made a perfunctory closing argument (taking up six pages of the trial transcript). The jury returned a verdict of death.
While his appeal in the capital case was pending, defendant petitioned this court for a writ of habeas corpus. We issued an order to show cause, appointed a referee, and directed the referee to make findings regarding defendant’s claim that he was denied effective assistance of counsel at trial.
At the habeas corpus reference hearing, defendant presented substantial evidence that trial counsel’s investigation, preparation, and presentation for *211the penalty phase of trial were grossly inadequate. Despite the availability of numerous family members who at the penalty phase could have offered mitigating evidence relating to defendant’s background and character that the jury may well have found persuasive, counsel failed to call even one such witness. Five of these witnesses testified at the reference hearing. Here, in summary, is what they said.
Teresa Mayfield, defendant’s cousin, testified that defendant was not a violent person, that he took care of and was very kind to her children, significantly helping one of them to overcome a speech problem, and that the two murders were out of character for him.
Trida Mayfield, defendant’s younger sister, also testified that the crimes were out of character for defendant. She described defendant as a kind and gentle person who had been protective of her as a child.
Calvin Hawkins, one of defendant’s uncles, stated that when he was disabled and in a wheelchair following a motorcycle accident, defendant was kind to him, provided him transportation, and took care of him for an extended period of time.
Cicero Mayfield, defendant’s younger brother, testified that defendant had helped him by teaching him how to avoid drugs and gangs. He was shocked when he learned of defendant’s arrest because the charges were inconsistent with defendant’s character and personality.
Hazel Hawkins, defendant’s mother, traced defendant’s problems to diabetes, which he developed at the age of nine. She stated that she had wanted to testify at trial to ask the jury to spare her son’s life.
In addition to these witnesses, the habeas corpus referee found that Willie Willingham, one of defendant’s uncles, who was deceased at the time of the reference hearing, would have testified to defendant’s disadvantaged childhood and given his view that defendant could overcome his personal and drug-related problems.
The record of the reference hearing further shows the availability of medical evidence relating to defendant’s insulin-dependent diabetic condition and his ingestion of PCP, and their possible effect on his behavior at the time of the crimes. Defendant’s trial counsel, however, never considered this mitigating evidence and consequently the jury never heard it. A summary of the testimony of these experts follows.
*212Dr. Clinton Young, an endocrinologist, stated that a diabetic with a blood-sugar level over 300 may experience blurred vision, impaired reasoning, dehydration and headaches, and that a blood-sugar level of 371 (defendant’s level following his arrest) may additionally produce fatigue and nausea. Dr. Young also mentioned defendant’s health problems, such as his refusal to eat properly, his refusal to take his insulin shots, and his numerous hospitalizations for poorly controlled diabetes, including a hospitalization one month before the killings.
Dr. David Smith, a toxicologist, testified that PCP “flashbacks” are common in a person who, like defendant, is diabetic. He explained that PCP is stored in the body’s fatty tissues and discharged later, causing a psychotic reaction, and that the acidification of blood and urine that occurs when a diabetic loses control may increase the amount of this discharge. Dr. Smith concluded that both the ratio of acidosis obtained from defendant when he was arrested (just hours after he committed the murders), and an acidification reading obtained from him four days later, were sufficiently high that PCP could have been released from defendant’s fatty tissues when he committed the murders. In Dr. Smith’s opinion, a combination of PCP abuse, alcohol abuse, out-of-control diabetes, and depression may have impaired defendant’s reasoning process and impulse control at the time of the crimes.
Dr. Rita Hargrave, a psychiatrist, related information regarding defendant’s childhood. In her view, defendant’s mental disorders, together with his diabetes and use of PCP, influenced his actions at the time of the crimes.
Dr. Guy Hunt, a neurologist, testified that killings were out of character for defendant and were the result of definite cerebral impairment. He added that the negative results of the computerized axial tomography (CAT) scan and electroencephalogram he had performed on defendant did not change his opinion.
The strength of the mitigating evidence relating to defendant’s background and character and his medical condition was such that, had it been presented, the jury may well have found it to extenuate the gravity of the crimes. Despite its availability, however, defendant’s trial counsel did not offer the evidence at the penalty phase. During the entire trial, counsel called only one witness on defendant’s behalf.
That sole defense witness was Dr. Craig Rath, a clinical psychologist, who testified at the penalty phase. On direct examination by defense counsel, Dr. Rath expressed his opinion that the two murders were “out of character” for defendant. He described defendant’s long history of diabetes, which included *21320 to 30 hospitalizations. Dr. Rath also testified to defendant’s remorse and to a report that had been prepared for defense counsel by Dr. Guy Hunt, a neurologist. From that report, Dr. Rath quoted Dr. Hunt’s conclusion that “the crime of which [defendant] is accused is out of character and can be explained only on the basis of definite cerebral impairment due to alcohol and drug abuse.”
In its cross-examination of Dr. Rath, the prosecution reviewed a number of psychological tests Dr. Rath had administered, highlighting that many of defendant’s specific responses on the tests contradicted the defense position. Dr. Rath acknowledged that two tests referred to in Dr. Hunt’s report, an electroencephalogram and a CAT scan, did not show any irregularities in the brain.
After conducting its redirect examination of Dr. Rath, the defense rested. The prosecution then called Dr. Soltz, a psychologist, as a rebuttal witness. Dr. Soltz was of the opinion that defendant’s mental condition was not abnormal, that he did not express remorse, and that he intended to kill when he committed the crimes.
As I have just shown, there is a substantial disparity between the strong mitigating evidence presented by the defendant’s appellate counsel at the reference hearing and the evidence that the defendant’s trial attorney actually presented to the jury at the penalty phase of defendant’s capital trial. Although this mitigating evidence was available to trial counsel, he called only one witness at the penalty phase, and that witness’s testimony was virtually nullified by the prosecution’s cross-examination and its rebuttal witness. As I shall discuss, trial counsel’s failure to present the mitigating evidence in question deprived defendant of his constitutional right to effective representation at the penalty phase of his capital trial.
II.
Under both the federal and state Constitutions, a criminal defendant is entitled to the effective assistance of counsel, that is, to counsel whose performance meets or exceeds an objective standard of reasonableness under prevailing professional norms. (Strickland v. Washington (1984) 466 U.S. 668, 688 [80 L.Ed.2d 674, 693-694, 104 S.Ct. 2052]; People v. Mincey (1992) 2 Cal.4th 408, 449 [6 Cal.Rptr.2d 822, 827 P.2d 388].) Effective representation requires that counsel adequately investigate, prepare, and present the defense. (In re Fields, supra, 51 Cal.3d at p. 1069; People v. Ledesma (1987) 43 Cal.3d 171, 215 [233 Cal.Rptr. 404, 729 P.2d 839].) It is particularly important in capital cases, which are often factually and legally *214complex, that courts ensure protection of the defendant’s constitutional right to a full defense. (Keenan v. Superior Court (1982) 31 Cal.3d 424, 430-431 [180 Cal.Rptr. 489, 640 P.2d 108].) Of course, the presentation of a full defense by competent counsel requires that the defense attorney focus the defense efforts on the issues to be determined by the trier of fact.
At the penalty phase of a capital trial, the jury is literally deciding a matter of life or death. “In explaining the jury’s role at the penalty phase, we have stated that the jury exercises an essentially normative task, acting as the community’s representative, that it may apply its own moral standards to the aggravating and mitigating evidence presented, and that it has ultimate responsibility for determining if death is the appropriate penalty for the particular offense and offender.” (People v. Edelbacher (1989) 47 Cal.3d 983, 1037 [254 Cal.Rptr. 586, 766 P.2d 1]; accord, People v. Karis (1988) 46 Cal.3d 612, 639 [250 Cal.Rptr. 659, 758 P.2d 1189]; People v. Williams (1988) 44 Cal.3d 883, 960 [245 Cal.Rptr. 336, 751 P.2d 395].) In carrying out this task, the jury must consider not only the nature of the offense, but also the background and character of the defendant (Penry v. Lynaugh (1989) 492 U.S. 302, 318-319 [106 L.Ed.2d 256, 277-278, 109 S.Ct. 2934]; Skipper v. South Carolina (1986) 476 U.S. 1, 4 [90 L.Ed.2d 1, 6-7, 106 S.Ct. 1669]), and any other circumstance that extenuates the gravity of the crime even though it is not a legal excuse for the crime. (Pen. Code, § 190.3, factor (k); People v. Brown (1985) 40 Cal.3d 512, 541 [220 Cal.Rptr. 637, 709 P.2d 440].) Here, trial counsel’s representation of defendant at the penalty phase was woefully inadequate.
As the habeas corpus referee commented in his report to this court, “[i]t is apparent . . . that [trial counsel] never gave much thought to a penalty phase.” The record of the reference hearing shows serious deficiencies in defense counsel’s investigation, preparation, and presentation of the defense at the penalty phase of defendant’s capital trial.
Defendant’s trial counsel either never interviewed, or only superficially interviewed, witnesses who could have offered strong mitigating evidence based on defendant’s background and character. As I set forth earlier, trial counsel never interviewed Teresa Mayfield (defendant’s cousin), Tricia Mayfield (defendant’s sister), or Calvin Hawkins (defendant’s uncle). The defense investigator’s interview of defendant’s brother, Cicero Mayfield, was so brief that it may fairly be characterized as nonexistent. With respect to Hazel Hawkins, defendant’s mother, the defense investigator’s interview focused on information adverse to defendant; the investigator never inquired into aspects of defendant’s background or character favorable to defendant.
The one significant interview trial counsel had with defendant occurred at the courthouse on the morning of the start of trial in this capital case. *215Counsel had, as the referee stated, “very superficial conversations at the courthouse” with defendant’s mother, Hazel Hawkins; with his uncle, Willie Willingham; and with Patricia Harper, whom the referee characterized as a key prosecution witness and who was also a friend of defendant’s and sympathetic to him. Trial counsel sought production of only a few of defendant’s medical records. He did not retain appropriate medical experts, such as an endocrinologist, toxicologist, or psychiatrist, who in this case could have provided testimony highly favorable to the defense.
Similarly insufficient was trial counsel’s preparation of the defense. As established at the habeas corpus hearing, counsel spent no more than 40 hours in out-of-court preparation on both the guilt and the penalty phases of this capital case. His trial file, from which nothing had been removed, contained no notes or legal research. He never listened to a tape-recorded statement prepared for him by Patricia Harper, who, as I explained above, was a key prosecution witness and also a friend of defendant’s and sympathetic to him. As the referee found, the “preparation was clearly inadequate.”
Trial counsel’s presentation of the defense case at the penalty phase of trial was likewise seriously lacking. Trial counsel stipulated at trial that the prosecution’s test results of a urine sample taken from defendant upon his arrest did not indicate the presence of any drugs. The urine sample was, however, never analyzed, although, as the referee found, a urine test is considered the most reliable indicator for PCP. Also, trial counsel did not call Dr. Guy Hunt, a neurologist, as a witness at the penalty phase. Dr. Hunt had performed a number of neurological tests on defendant and had prepared a report. The report states Dr. Hunt’s conclusion that ‘the crime of which [defendant] is accused is out of character and can be explained only on the basis of definite cerebral impairment due to alcohol and drug abuse.” Thus, Dr. Hunt could have assisted the defense in persuading the jury that defendant’s worth as an individual should not be judged solely by his commission of the capital murders, shocking as they were, because the murders occurred while defendant was in an abnormal state.
At the habeas corpus reference hearing, trial counsel was unable to present a viable excuse for his failure to adequately investigate, prepare, or present the defense case; his attempts to offer an explanation were simply not credible. For example, he said he did not call Dr. Hunt, the neurologist, as a witness at defendant’s capital trial because Dr. Hunt had told counsel his testimony would have a “devastating” effect on defendant’s case. Counsel stated he did not ask Dr. Hunt about the nature of the “devastating” information. Dr. Hunt, however, denied making the statement in question, and the referee found counsel’s story implausible. The referee concluded *216that Dr. Hunt did not possess any “devastating” information pertaining to defendant, and that Dr. Hunt had put all of the material information he had in his report to defendant’s trial counsel. On this issue, the referee stated, “[t]his court simply cannot imagine an attorney defending a capital case and blinding himself to ‘devastating’ information.” With respect to counsel’s failure to call Willie Willingham, one of defendant’s uncles, as a witness at trial, counsel stated at the reference hearing that he thought Willingham had a felony record. In fact, Willingham did not have a felony record.
Counsel’s minimal presentation at the penalty phase of defendant’s capital trial cannot be justified as a tactical decision. An informed and rational decision based on strategy and tactics can be made only after adequate investigation and preparation. (See, e.g., In re Fields, supra, 51 Cal.3d at p. 1069; People v. Ledesma, supra, 43 Cal.3d at p. 215.) Here, because his investigation and preparation were seriously inadequate, counsel was unaware of much of the potentially mitigating evidence that existed. Therefore, it cannot be said that counsel’s failure to present that evidence was an informed tactical choice.
Counsel’s grossly inadequate performance at the penalty phase denied defendant his constitutional right to effective representation. The prosecution’s legal expert, a prosecutor who knew defendant’s trial counsel, succinctly described trial counsel as “the type of attorney who seeks to win his cases by inspiration, not perspiration; by oration, not preparation.” In this case, counsel’s inspiration and oration were not enough. As I shall discuss, trial counsel’s failings were prejudicial. The mitigating evidence that a competent attorney would have presented was significant enough, in the context of other evidence bearing on penalty, that confidence in the outcome—the verdict of death—is substantially undermined.
III.
To obtain relief on the basis of ineffective assistance of counsel at the penalty phase, a defendant “need not show that counsel’s deficient conduct more likely than not altered the outcome in the case.” (Strickland v. Washington, supra, 466 U.S. at p. 693 [80 L.Ed.2d at p. 697].) Instead, the defendant is entitled to a reversal of the penalty phase if the ineffective assistance of counsel “undermine[s] confidence” in the verdict of death. (Id. at p. 694 [80 L.Ed.2d at p. 698]; In re Fields, supra, 51 Cal.3d at pp. 1078-1079.)
Here, as I discussed in detail earlier, trial counsel’s investigation, preparation and presentation at the penalty phase were so grossly inadequate as to *217undermine any reasonable confidence in the verdict of death. Counsel’s inadequacies precluded the jury from ever learning of substantial mitigating evidence of defendant’s background and character, and medical condition. The majority nevertheless concludes that it “need not give weight to deficiency [of trial counsel] when we conclude that there was no prejudice.” (Maj. opn., ante, at p. 200.) The majority asserts that trial counsel’s performance was not prejudicial because at the habeas corpus reference hearing the defense witnesses were asked “devastating questions” on cross-examination that if asked at trial “would have revealed to the jury specific instances of [defendant’s] uncharged violent criminal acts . . . .” (Maj. opn., ante, at p. 207.) Not so.
The testimony at the habeas corpus reference hearing does not support the majority’s assertion. As the referee found, “[m]any of the uninterviewed lay witnesses did not have negative information regarding [defendant].” This finding is confirmed by a review of the prosecution’s cross-examination of a number of the witnesses at the reference hearing.
At that hearing, a major point that the prosecution sought to make in its cross-examination of defendant’s relatives—Teresa Mayfield, Tricia May-field, Calvin Hawkins, Cicero Mayfield, and Hazel Hawkins—was that these witnesses did not more affirmatively seek out defendant’s trial counsel or inject themselves into the defense of the case. Unlike the majority, I do not find this cross-examination “devastating”; it is legally meaningless. It is the attorney who has the obligation to investigate and prepare. (In re Fields, supra, 51 Cal.3d at p. 1069.) The law does not require potential witnesses to seek out trial counsel, marshall the pertinent facts for counsel, or otherwise develop the defense.
To support its assertion that defendant’s trial counsel’s ineffective representation at the penalty phase was not prejudicial because of the prosecution’s “devastating” cross-examination of the defense witnesses at the habeas corpus reference hearing, the majority refers to evidence of a single incident of “a disturbing sexual nature.” (Maj. opn., ante, at p. 207.) The majority’s implication of prior serious sexual misconduct by defendant that would have driven the jury to impose the death penalty overstates both the facts and the potential impact this incident may have had on the jury.
The incident occurred when defendant was 11 years old, 10 years before the commission of the crimes in this case. It was based on defendant’s mother finding him with his pants down on top of his two-year-old sister with her dress pulled up. The sister, who was examined by defendant’s mother both immediately after the incident and the next morning, showed no *218outward signs of sexual molestation. Defendant told his mother at the time that he did what he did because two other eleven-year-old children in the neighborhood had suggested he do so.
This particular evidence has minimal probative value in the decision whether to sentence defendant to death for the two murders he committed. Defendant was a young child at the time; the incident happened 10 years before the crimes in this case. And, contrary to the majority’s assertion, the incident, although disturbing, is not “devastating,” as the following excerpt from the prosecution’s cross-examination of Tricia Mayfield indicates. “[Question] You think it is normal for, say, a 10-year-old to try to have sex with a three-year-old? [][] [Answer] I don’t think it is normal, but I don’t think it is abnormal either, [ft] [Question] Is that something you heard happened among family members? [1] [Answer] That’s not unfamiliar to any race in any part of the nation, [ft] [Question] So you think that is a perfectly normal thing to have happened? [ft] [Answer] I think perfectly normal to have a 10-year-old to wonder about sex with a sister or friend or whatever, [ft] [Question] The question is do you think it is normal for a 10-year-old to try to have sex with his sister? [1] [Answer] Not normal. But like I said, [it is] not abnormal either.”
Given the minimal probative value of this childhood incident, it is doubtful it would have had much, if any, impact on the jury. For the same reason, it is doubtful that, had defendant’s trial counsel considered the matter,2 the evidence would have been presented to the jury. The minimal probative value of the evidence provides an ample basis for it to have been excluded at trial. (Evid. Code, § 352.) Indeed, it is questionable whether the prosecutor would have even tried to introduce such evidence. As the just-quoted cross-examination of Tricia Mayfield at the habeas corpus reference hearing demonstrates, introduction of this evidence by the prosecution was not without its tactical risks. For the reasons I have articulated, I find the majority’s reliance on this childhood incident to be seriously misplaced.
Equally wrong is the majority’s assertion that the defense experts who testified at the habeas corpus reference hearing were subject to “devastating” cross-examination by the prosecution. A review of the cross-examination of Drs. Hunt, Young, Smith, and Hargrave at the reference hearing does not support this assertion. To the extent the majority means to refer to expert testimony that a person in defendant’s situation could form the intent to kill *219and premeditate murder, the majority confuses the issues at the guilt phase with the much broader issues at tibe penalty phase. Under California’s capital punishment law, the issues at the penalty phase include defendant’s character and background and any other consideration that tends to extenuate the gravity of the offense. (§ 190.3, factor (k).) The testimony of defendant’s expert endocrinologist, neurologist and psychiatrist spoke directly to matters the jury should have considered—whether his long-term diabetes, substance abuse and psychiatric problems made defendant less deserving of society’s ultimate penalty, and a better candidate for the penalty of life in prison.
IV.
The choice between life and death at the penalty phase of a capital case is the most serious decision a jury can be asked to make. “The United States Supreme Court has expressly recognized that death is a different kind of punishment from any other, both in terms of severity and finality. Because life is at stake, courts must be particularly sensitive to insure that every safeguard designed to guarantee defendant a full defense be observed, (Gardner v. Florida (1977) 430 U.S. 349, 357 [51 L.Ed.2d 393, 401-402, 97 S.Ct. 1197][.])” (Kennan v. Superior Court, supra, 31 Cal.3d at p. 430.) Here, the strength of the evidence adduced at the habeas corpus reference hearing, when compared to the evidence presented at the penalty phase and the depth of the inadequacies of defendant’s trial counsel, thoroughly undermine any reasonable confidence in the verdict of death. Had trial counsel adequately presented the defense at the penalty phase, it cannot be concluded that the result—a verdict of death—would have been the same. In such circumstances, we must put aside any personal beliefs as to the propriety of the penalty of death, and allow the jury to make its own decision based on all the evidence, presented by competent counsel.
I would issue the writ of habeas corpus, vacate the sentence of death, and direct a retrial of the penalty phase.
Appellant’s petition for a rehearing was denied July 21, 1993, and the opinion was modified to read as printed above. Mosk, J., and Kennard, J., were of the opinion that the petition should be granted.
Although counsel’s representation of defendant throughout the trial was inadequate, I agree with the majority that the inadequacy was harmless at the guilt phase. Nevertheless, I have set forth some facts relating to counsel’s inadequate efforts at the guilt phase to demonstrate that counsel’s representation was inadequate throughout defendant’s trial, not merely at the penalty phase, and to show that this is not a case in which counsel’s failure to present mitigating evidence at the penalty phase of trial was offset by the introduction of such evidence at the guilt phase. (See, e.g., In re Fields (1990) 51 Cal.3d 1063, 1080 [275 Cal.Rptr. 384, 800 P.2d 862].)
It appears from trial counsel’s testimony at the reference hearing that he believed the incident to have occurred closer in time to defendant’s commission of the offenses in this case. Had counsel investigated, he would have learned that the incident took place when defendant was a young boy 10 years earlier.