In March 2000, a tough guy named Petros Bedi was convicted of shooting a man dead in an Astoria nightclub. For this and other crimes, he is now serving 42 1/2 years in prison.

The crucial witness against Mr. Bedi agreed to testify only after the police arrested him on charges of dealing drugs.

During Mr. Bedi’s trial, a defense lawyer blasted away at the credibility of this witness and tried to prove he had incentive to lie. Didn’t the Queens district attorney foot the hotel bill to put up you and your girlfriend for eight months? Weren’t you paid handsomely for your testimony?

No, the witness insisted. I paid my own bill. Nobody paid me anything.

This was not true, and the prosecutors who sat in that courtroom and vouched for the honesty and truthfulness of this witness knew it.