Appeal by defendant from a judgment of the Supreme Court, Kings County, rendered September 21, 1977 and October 4, 1977, convicting him of assault in the first degree and criminal possession of a weapon in the fourth degree, upon a jury verdict, and imposing sentence. Judgment reversed, on the law and as a matter of discretion in the interest of justice, and new trial ordered. Defendant was charged, inter alia, with assault in the first degree as a result of a stabbing incident. The defendant testified in his own defense and, on cross-examination, the prosecutor repeatedly tried to have him state that a police witness was a liar. On summation, the prosecutor commented that if the defendant stuck to his story "he would be calling Detective Doyle a liar”. Thereafter, he proceeded to vouch for the officer’s testimony. This court has repeatedly condemned such questions and comments by the prosecution as prejudicial (see, e.g., People v Yant, 75 AD2d 653; People v Diaz, 73 AD2d 604; People v Lopez, 73 AD2d 676). Besides improperly questioning the defendant as to whether the police were lying, the prosecutor’s vouching for the police officer’s testimony constituted improper bolstering (see People v Perez, 69 AD2d 891; People v Webb, 68 AD2d 331). In addition, the prosecutor’s denigration of the defense witnesses’ testimony was improper (see People v Shanis, 36 NY2d 697; People v Webb, supra). The fact that defense counsel failed to object to some of the prosecutor’s questions or comments does not preclude this court from ordering a new trial as a matter of discretion in the interest of justice (see People v Butler, 57 AD2d 931). In addition, we note that the prosecutor improperly cross-examined the defendant’s character witness as to his actual knowledge of particular acts of misconduct (see People v Kennedy, 47 NY2d 196; People v Alamo, 23 NY2d 630, cert den 396 US 879) and the trial court improperly questioned the defendant and made comments concerning an alleged eyewitness (cf. People v De Jesus, 42 NY2d 519; People v Bell, 38 NY2d 116). Damiani, J. P., Gulotta, Martuscello and O’Connor, JJ., concur.