dissenting:
I am unable to agree with the majority that the trial court did not err in restricting appellant’s right to cross-examine the prosecuting witness, Robert Moore, on his motive for testifying.
It is of course settled that the scope of cross-examination is largely within the discretion of the trial court, and that its action will not be reversed in the absence of an abuse of discretion or error of law. Commonwealth v. Cheatham, 429 Pa. 198, 239 A.2d 293 (1968). However, it is equally settled that the right to cross examination “is encompassed by the accused’s right of confrontation in a criminal case, as protected by the Sixth Amendment,” Commonwealth v. Greene, 469 Pa. 399, 404, 366 A.2d 234, 236 (1976), and that the right of confrontation includes the right to cross examine a witness on his possible motive for testifying, Davis v, Alaska, 415 U.S. 308, 94 S.Ct. 1105, 39 L.Ed.2d 347 (1974); Commonwealth v. Dawson, 486 Pa. 321, 405 A.2d 1230 (1979). In the present case, in my opinion appellant was deprived of this right when the trial court sustained the prosecutor’s objection to the following question, asked by defense counsel when cross-examining Robert Moore:
Q: Did you ever ask the Assistant District Attorney to see Mr., Mr. Coll, to see whether it would be possible for you to get a reduction of sentence in return for your testimony-
MR. HARRIS (Assistant District Attorney): Objection.
BY MR. STEDJE (Attorney for Defendant)
Q: “-about William Baker?”
(N.T. 63)
It is evident that defense counsel had a basis in fact for his cross-examination. Appellant had been tried on the same charge on May 23-24,1977, before the Hon. Joseph W. DE FURIA. The trial had resulted in a “hung jury” and consequently a mistrial. During this first trial, Moore testified that appellant had held a razor to his throat on two occasions, but had not committed any sexual assaults upon *231him. (5/23-24/77 N.T. 21-26) On redirect examination by the Assistant District Attorney, Moore testified that he feared retaliation from other inmates or appellant if he testified further about the assaults on him. (5/23-24/77 N.T. 34r-35) Moore later testified that during a recess in the trial, he had asked to see the Assistant District Attorney to get protection from threats of retaliation. (5/23-24/77 N.T. 36) He then changed his testimony and stated that in fact appellant had committed sexual assaults on him. (5/23-24/77 N.T. 44r-48) This change in testimony lead to the following cross-examination by defense counsel:
Q: Now, Mr. More, [sic] why are you changing your testimony today?
A: I was guaranteed protection.
Q: Pardon me?
A: I was guaranteed protection.
Q: By whom?
A: People who work in the District Attorney’s office.
Q: What does that mean to you?
A: Oh, I think I can trust them.
Q: Have you asked the District Attorney to be taken out of a specific penal institution located in the State of Pennsylvania?
A: No, I didn’t.
Q: Have you had any conversations with any District Attorneys concerning the terms of your present incarceration at Camp Hill?
A: No, I haven’t.
Q: Do you remember Mr. Coll asking you when you first testified today that something to the effect are you asking for immunity or a reduction in your current sentence in return for your testimony? Do you remember him asking you that?
A: Yes.
Q: Why would he ask you a question like that, Mr. More, if you hadn’t had a conversation with him concerning that subject, do you know?
*232A: No.
Q: You are testifying under oath today that you never had such a conversation with Mr. Coll; is that correct?
A: Before I came up on the stand I asked him could anything be done? He said he would let me know later. There was no conversation.
Q: When did that question from you occur, Mr. More, do you remember?
A: Yes, before I came up on the stand the first time.
Q: And, what did you say to him specifically?
A: Could anything be done about it.
Q: Were those your words, that is my question, were they your words?
A: Yes.
Q: Mr. Coil’s response to you was what?
A: He would let me know later.
Q: Well now what did you mean or what did you understand Mr. Coil’s statement to you to mean in response to your question? You said what he told you.
A: When he said he would let me know later, I took for granted he would talk to the Judge and see what the Judge said, and whatever the Judge said would go.
Q: Do you feel that by testifying today in Court against William Baker that you could obtain some kind of adjustment of your sentence as a result of your conversation with Mr. Coll?
Do you still have that hope?
A: Excuse me?
Q: Yes.
In response to your question Mr. Coll told you that he would see what could be done later.
Did you understand that to mean that if you testified today against William Baker you would receive consideration at some future time concerning your present incarceration, favorable consideration?
*233A: No.
Q: I Ask you again, Mr. More, isn’t the reason you brought these charges against Mr. Baker to get consideration?
MR. COLL: I object, your Honor. These are argumentative questions at this point.
THE COURT: It is cross-examination.
Overruled.
THE WITNESS: No, it is not my point.
(5/23-24/77 N.T. 57-60)
In short: At appellant’s first trial, the court permitted cross-examination of Moore on his possible motive for testifying against appellant; at appellant’s second trial, the court forbid such cross-examination.
The majority states that Moore “no longer had anything to gain by falsifying his testimony. Once the sentence was imposed [i. e., Moore’s sentence on his own conviction], his perception of what might be done on his behalf was quite immaterial.” At 696. I admit to being unable to understand this statement. Does the majority mean that Moore’s “perception of what might be done for him was quite immaterial” because, his sentence having been imposed, in fact the Commonwealth could do nothing to him? If that is what the majority means, it is mistaken in two respects. First, in deciding whether a witness is biased, the issue is not whether the witness’s “perception” is right or not; the issue is whether the perception exists. For example, the witness may be entirely mistaken that the defendant has caused him to be fired, or has stolen his wife’s affections; if, however, he nevertheless thinks the defendant has done either of these things, he may be biased against the defendant, and defense counsel is entitled to demonstrate that bias on cross-examination. Here, Moore’s possible perception that the Commonwealth could help him if he testified against appellant at appellant’s second trial may have been entirely mistaken, but that does not mean, as the majority seem to think it does, that he could not be cross-examined regarding his (mistaken) perception. Second, it is by no means evident *234that Moore’s perception was mistaken. Having sought the Commonwealth’s favor once, at appellant’s first trial, he may well have believed correctly that if he did not again testify against appellant, the Commonwealth would be able to hurt him, as for example by having him transferred to another prison that he did not want to go to, or by objecting to his parole, or, conversely, that the Commonwealth would be able to help him, as for example by having him transferred to another prison that he did want to go to, or by not objecting to his parole. In either case, the cross-examination should not have been forbidden:
A more particular attack on the witness’ credibility is effected by means of cross-examination directed toward revealing possible biases, prejudices, or ulterior motives of the witness as they may relate directly to issues or personalities in the case at hand. The partiality of a witness is subject to exploration at trial, and is ‘always relevant as discrediting the witness and affecting the weight of his testimony. Davis v. Alaska, 415 U.S. 308, 316, 94 S.Ct. 1105, 1110, 39 L.Ed.2d 347 (1974).
The trial court’s error in prohibiting cross-examination on Moore’s possible motive for. testifying was not harmless beyond a reasonable doubt. Error is harmless only when the appellate court can determine that the error could not have contributed to the verdict. Commonwealth v. Story, 476 Pa. 391, 383 A.2d 155 (1978). Where there is a “reasonable possibility” that an error “might have contributed to the conviction,” the error is not harmless. Commonwealth v. Davis, 452 Pa. 171, 178, 305 A.2d 715, 719 (1973), quoting Chapman v. California, 386 U.S. 18, 24, 87 S.Ct. 824, 828, 17 L.Ed.2d 705 (1967). Here, it is reasonably possible that the trial court’s prohibition of cross examination on Moore’s motive for testifying may have contributed to appellant’s conviction. Had the jury been allowed to hear defense counsel question Moore about his requests to the Commonwealth for favored treatment, they might have discredited his testimony incriminating appellant. This supposition is corroborated by the fact that at appellant’s first trial the jury was unable to agree. As the only witness to testify as *235to the two assaults upon him by appellant, Moore’s testimony was essential to the Commonwealth’s case against appellant.* Without Moore’s testimony, it seems likely that there would not have been sufficient evidence to support a verdict against appellant. In these circumstances it cannot be maintained that the trial court’s error was harmless beyond a reasonable doubt.
I should reverse and remand for a new trial.
The only other witness to the assault was Nathaniel McNair, a fellow inmate who testified that he saw Moore and appellant in appellant’s cell on September 16 and 21 of 1976, and that on the latter date he saw appellant’s feet in a position behind Moore so as to lead him to conclude that the two were engaging in a sexual act. (9/6-12/77 N.T. 127) However, McNair testified that he did not want to testify further as to what he saw on either date for fear of physical retaliation by appellant or other prisoners acting on his behalf. (9/6-12/77 N.T. 104-119)