The defendant in a criminal case has both a United States and Pennsylvania Constitutional right to confront and cross‑examine Commonwealth witnesses. That constitutional right includes the right to cross‑examine Commonwealth witnesses regarding their biases and motives. The Pennsylvania Supreme Court held "whenever a prosecution witnesses may be biased in favor of the prosecution because of outstanding criminal charges or because of any non‑final criminal disposition against him within the same jurisdiction, that possible bias, in fairness, must be made known to the jury." Commonwealth v. Evans, 512 A.2d 626 (Pa. 1986).A witness' motivation in testifying is a proper and important function of the constitutionally protected right of cross‑examination.. It is undisputed trial judges retain wide latitude insofar as the Confrontation Clause is concerned to impose reasonable limits on such cross‑examination. The pertinent case law, however, permits a police witness to be cross‑examined about misconduct as long as the wrongdoing is in some way related to the defendant's underlying criminal charges and establishes a motive to fabricate.
For instance, a police witness had been demoted after it was discovered he repeatedly took bribes; defendant was improperly restricted from impeaching him with this evidence since it bolstered entrapment defense in defendant's bribery prosecution. Similarly, a police officer was under investigation at trial and had been demoted for beating defendant's co‑defendant; defendant should have been permitted to question the officer about the matter since it provided officer with motive to obtain conviction against defendant as well as to fabricate fact that defendant had confessed. Lastly, the defendant was awarded a new trial because he had not been permitted to impeach officer with fact that he was part of group of police officers who were racially biased, made false arrests, and perjured themselves in criminal prosecutions.