Ordered that the order is reversed, on the law, without costs or disbursements, the fact-finding order is vacated, and the matter is remitted to the Family Court, Kings County, for a new fact-finding hearing.
The court improperly prevented the appellant's Law Guardian from questioning the presenting agency's main witness as to whether he had previously burglarized the complainant's apartment. It is well settled that a witness may be interrogated upon cross-examination with respect to any immoral, vicious, or criminal acts which may affect his character and show him to be unworthy of belief, provided the cross-examiner questions him in good faith and upon a reasonable basis in fact (see, People v Jones, 193 A.D.2d 696; People v. English, 126 A.D.2d 738; People v Allen, 67 A.D.2d 558, 560, affd 50 N.Y.2d 898).
In the present case, the Law Guardian established a good faith basis for the question, and the information sought reflected upon the witness's credibility. Since the witness was the only witness to identify the appellant as one of the perpetrators of the burglary and the Law Guardian set forth the theory that the witness may have been involved in the burglary, we cannot say that this error was harmless (see, People v. Jones, 193 A.D.2d 696, supra). Bracken, J.P., Rosenblatt, Lawrence, Krausman and Goldstein, JJ., concur.