(dissenting) — I agree with the court’s disposition of all of the questions presented on this appeal, save one. That is the question whether the trial court erred in refusing to admit the opinion of a psychiatrist concerning the appellant’s ability to form the specific intent to commit the crimes charged. The offered opinion was based on the appellant’s testimony describing the amount and kinds of drugs and alcohol which he recalled having consumed on the day of the crimes.
The majority says that the appellant’s testimony about his activities on the day in question was so vague that no valid opinion could be based upon it. The trial court did not find it that insubstantial. It allowed the witness to give his opinion at some length but would not let him give an opinion on what it termed the “ultimate issue.”
*761It seems to me that the appellant’s testimony could be hardly precise and cogent if he did in fact consume a large quantity of stimulants, depressants, and disorienting drugs. But it was the jury’s function to weigh this testimony. It is not a proper function of this court. The trial court did not exclude the doctor’s opinion because it was based on vague testimony. Its refusal was based solely on its conclusion that such an opinion would be an opinion on the “ultimate question” to be decided by the jury. The trial court thought that an expert opinion on the “ultimate issue” is inadmissible as a matter of law.
It is clear that the trial court was in error in this. An expert may testify about the mental condition of a defendant at the time of the commission of an alleged crime. State v. Bridgham, 51 Wash. 18, 97 P. 1096 (1908); and see State v. White, 60 Wn.2d 551, 374 P.2d 942 (1962), at 575-581.
We held in State v. Alden, 73 Wn.2d 360, 438 P.2d 620 (1968), that the opinion of a qualified expert, if it will aid the jury in reaching its verdict and will not mislead it to the prejudice of the objecting party, is proper evidence even though it may be an opinion on the “ultimate issue.”
The respondent and the majority tacitly recognize the validity of this principle, since they do not offer to support the trial court’s ruling on the ground which the court itself gave for making that ruling.
The case cited by the majority, State v. Farley, 48 Wn.2d 11, 290 P.2d 987, cert. denied, 352 U.S. 858, 1 L. Ed. 2d 65, 77 S. Ct. 79 (1955), is obviously not in point. There the medical expert was asked to give an opinion regarding the defendant’s mental state at the time of the alleged crime. The opinion would have been based solely on the doctor’s subsequent examination of the defendant. The case does not hold that a psychiatrist cannot give an opinion concerning the mental condition of a defendant at the time of an alleged crime, based upon the testimony of the defendant concerning his acts and other conditions which may have affected his mental state. An expert opinion based on the testimony of a witness is admissible. State v. McKeown, 172 Wash. 563, 20 P.2d 1114 (1933).
*762This is a capital case 'and the presumption should not be indulged that any error which occurred was harmless error. I am dismayed by implications in the majority opinion that, if this court is convinced by the state’s evidence, it will hold the erroneous exclusion of the appellant’s offered evidence to be harmless and nonprejudicial. It is not this court which must be convinced of the appellant’s guilt. It is the jury. And the appellant was entitled to have the jury consider any relevant, competent, and material evidence which he offered in his defense, if that evidence was not otherwise inadmissible by reason of some affirmative rule of law.
Here the rule is, as the majority concedes, that intoxication or mental derangement, even though self-induced, is a defense if it renders the defendant incapable of forming the specific intent which the state must prove in order to warrant a conviction.
The appellant offered medical evidence in the form of a psychiatrist’s opinion that, if he had ingested all of the substances which he claimed to have consumed on the day of the crimes, he would have been incapable of forming such an intent. That opinion should have been received in evidence, the court having found the doctor qualified to give opinions based on the appellant’s testimony, however vague that testimony may have been.
If the appellant’s testimony concerning his activities was improbable, the jury could be expected to reject it, and with it, the psychiatrist’s opinion based upon it. But it is not for this court to reject it or to say that the state’s case was proved beyond a reasonable doubt. It is difficult to imagine that the jury would have found the appellant incapable of forming the intent necessary to commit the crimes which the evidence tends to show he did commit, and I strongly suspect that, if asked the question on cross-examination, the doctor would have testified that if the appellant had been sufficiently drugged to lose the ability to form an intent, he would have been unable also to coordinate sufficiently to do the acts involved in the crimes. However, there is no testimony to this effect in the record. One can only speculate as to how well the opinion would *763have been tested and how well it would have stood up at the trial. It cannot be said, on the record before us, that the error in rejecting the official evidence was harmless. The appellant was entitled to have the jury consider such evidence as he was able to muster in his own defense.
In my opinion, the refusing of this evidence was prejudicial error and a new trial should be granted.
Hunter, C. J., and Neill, J., concur with Rosellini, J.
May 27,1970. Petition for rehearing denied.