*264Concurring Opinion by
Mr. Justice Roberts:I concur in the result reached by the majority. However, it is my view that the disposition of this case is controlled by this Court’s recent decision in Commonwealth v. Haideman, 449 Pa. 367, 296 A. 2d 765 (1972). Although Haideman and the instant case are factually distinguishable,* the evil to be protected against is the same. In both cases, the prosecution attempted to create the impermissible inference that the accused’s silence at the time of arrest may be taken as an expression of guilt. Haideman laid to rest any suggestion that such an inference is constitutionally permissible.
Moreover, I must disagree with the majority’s holding that the violation in this case of the well-established rule that a party cannot plead surprise, and then proceed to cross-examine and impeach its own witness by use of prior statements when the witness cannot recall or remember matters which he spoke of with certainty before trial is harmless error. Surely it can never be harmless error when, as on this record, the improperly admitted evidence substantially and significantly advances the Commonwealth’s case by undermining the defense.
Appellant was charged with conspiracy and murder. The Commonwealth tried to prove, on the basis of the testimony of two alleged accomplices, that appellant and three others were drinking together at a bar, and shortly thereafter accosted and murdered the victim. *265When the bartender testified for the defense that appellant was not at the bar the night of the crime, the Commonwealth called one Betty Gary to rebut this evi dence. She testified that she could not remember and was not sure whether appellant was present at the bar. The Commonwealth then pleaded surprise, and over objection introduced for the purposes of impeachment her prior written statements that she had seen appellant at the bar the night of the crime.
The majority, in the instant case, quoting from Knudsen properly notes: “. . . our courts have been loath to allow cross-examination for purposes of impeachment by use of prior statements when a witness states that he does not know or that he cannot remember. This is so for the reason that such an in-court declaration does not harm the calling party nor aid the opposing party. . . . Hence, when a witness claims he does not know or cannot remember, the prior statements should not be introduced because of the danger that the prior statements will be considered as substantive evidence by the jury.” Commonwealth v. Knudsen, 433 Pa. 412, 414-15, 278 A. 2d 881, 883 (1971) (citations omitted) ; see Commonwealth v. Turner, 389 Pa. 239, 256, 133 A. 2d 187, 195 (1957).
In Turner, supra, a co-defendant had been the principal Commonwealth witness at Turner’s prior trial but after the trial that co-defendant denied anything to do with the crime. He further denied having any knowledge of Turner’s participation in the crime. In spite of this recantation, the Commonwealth called the co-defendant to testify at the trial, pleaded surprise and was permitted to introduce his prior testimony. This Court, in reversing the conviction held: “It is wholly unrealistic to pretend that the jury was capable of eradicating from their minds Lofton’s former testimony except for its effect in currently impeaching him. Even *266if the jurors tried ever so conscientiously to so limit the effect of the witness’s prior testimony and concluded that, by reason thereof, he was not presently worthy of belief, the resultant psychological effect would be to cause the jury to deduce that what Lofton had first testified to was the truth. The harm to the defendant from the improper cross-examination is . . . manifest. . . .” Commonwealth v. Turner, 389 Pa. 239, 256, 133 A. 2d 187, 195 (1957).
In Knudsen, supra, and Commonwealth v. Linkowski, 363 Pa. 420, 70 A. 2d 278 (1950), this Court regarded as harmless error the admission of impeaching statements after a witness could not recall or remember matters which he spoke of with certainty before trial. Unlike the case at hand, both of those cases involved the erroneous admission of impeachment evidence which was oiot central to the determination of the key questions in dispute. In Knudsen, supra, the challenged impeaching statement tended to prove the premeditation requisite for murder, but the jury found the defendant guilty only of involuntary manslaughter. In Linkowski, admission of the impeaching statement Avas held to be harmless error “inasmuch as this testimony dealt only with the fight which, although important to supply motive, is not disputed, the real question being the identity of the slayer.” Id. at 424, 70 A. 2d at 280.
Here, however, the Commonwealth’s case depends to a large degree on proof that appellant, together Avith three other defendants, visited the bar shortly before the murder. The key element in appellant’s defense was the bartender’s testimony that appellant was not at the bar on the night of the crime. Other than appellant’s tAvo alleged accomplices, Betty Gary was the only Commonwealth witness offered to rebut the bartender’s testimony. The erroneously admitted prior *267statement went to tbe heart of one of the key questions in dispute.
Thus, by the erroneous admission of the prior statement, the jury’s verdict was fully subject to the “'danger that the prior statements will be considered as substantive evidence by the jury.” Commonwealth v. Knudsen, 433 Pa. 412, 415, 278 A. 2d 881, 883 (1971). Here, as in Turner, . . the harm to the defendant from improper cross-examination is . . . manifest. . . .” Commonwealth v. Turner, 389 Pa. 239, 256, 133 A. 2d 187, 195 (1957).
Although the majority properly recites the controlling law as enunciated in Turner and Knudsen, supra, it applies these principles, on this record, incorrectly.
Here, defendant testified, on direct examination, that Re Rad been warned of Ris lights at tRe time of arrest, and as a result, cRose to remain silent. TRe prosecution, in its closing argument, seized on this assertion, and attempted to create in tRe minds of tRe jurors tRe inference tRat tRe defendant’s silence should be taken as a manifestation of guilt.
In Haideman, tRe prosecution, during its case in chief, through the testimony of the arresting officer, attempted to create the same inference.