See State v. Mosley: http://appellate.nccourts.org/opinions/?c=2&pdf=MjAxMC8wOS0xMDYwLTEucGRm
A criminal defendant has a constitutional right to cross-examine and confront the State's key witness about his pending charges. State v. Prevatte, 346 N.C. 162, 163, 484 S.E.2d 377, 378 (1997) (citing Davis v. Alaska, 415 U.S. 308, 315, 94 S. Ct. 1105, 1110 (1974)). In Prevatte, the defendant sought to cross-examine the State's principal eyewitness against him about the witness' pending forgery and uttering charges in another county. Prevatte, 346 N.C. at 163, 484 S.E.2d at 378. The trial court prohibited the defendant from cross-examining the witness about the charges and, relying on Davis v. Alaska, the North Carolina Supreme Court held the trial court erred. Id. The Court stated the effect of the handling of the witness' pending charges was for the jury to determine. Id. At 164, 484 S.E.2d at 379.
In Davis v. Alaska, the State of Alaska sought to limit the defendant's cross-examination of a State's witness about his probationary status. Davis, 415 U.S. at 311, 94 S. Ct. at 1108. The trial court sustained the State's objection and did not allow the defendant to cross-examine the witness about his probationary status. Id. The Supreme Court reversed, however, on the grounds that the trial court's limitation of the defendant's cross-examination denied the defendant's constitutional right to confront witnesses against him. Davis, 415 U.S. at 315-318, 94 S. Ct. at 1110-1111. The United States Supreme Court said the purpose of cross-examination is not just to test a witness' memory and perception of an event, but also to impeach and discredit the witness. Davis, 415 U.S. at 316, 94 S. Ct. at 1110. To impeach a witness, a defendant is entitled to show bias and prejudice. Id.