A prosecutor says he has gathered overwhelming evidence against an alleged police killer, right down to the piece of chicken the suspect was eating before the shooting. But the trial may never take place because detectives lied to obtain a search warrant.

On Monday, Suffolk Superior Court Judge Charles Grabau is scheduled to hold a hearing to decide whether Albert Lewin, 33, will be charged in the shooting of a Boston detective during a raid on a drug dealer's apartment 13 months ago.The detective, 36-year-old Sherman Griffiths, was felled by a bullet that pierced the apartment's steel-reinforced door as members of Boston's elite anti-drug task force prepared to break it down.

Grabau dismissed the original charges against Lewin two weeks ago after detectives failed to produce a potential defense witness, the informant who supposedly led them to the apartment where the shooting took place.

In a remarkable turnabout in their story, the three detectives, under pressure from the prosecutor, filed affidavits Monday admitting that the informant they called "John" never existed.

Assistant District Attorney Francis O'Meara, in asking Grabau to change his mind and reinstate the charges, said he will argue Monday that the evidence against Lewin is so overwhelming that the misconduct by police should not block the prosecution.

By the time the officers finally got into the apartment, the killer had fled down a back stairway. But the evidence that Lewin had been in the apartment is strong, said O'Meara.

"I've got his fingerprints in there, I've got his clothes in the closet, I've got his cigarettes, I've got his foot powder. I've even got the piece of chicken that he was eating 20 minutes before the raid," O'Meara said.

Lewin's defense attorney, Max Stern, contends that the detectives' misconduct has permanently prevented his client from getting a fair trial.

"The critical witnesses, the police officers themselves, have completely trumped themselves and the (prosecution's) case by their massive and repeated perjury in the case, which they now admit to," Stern said. "They have lied so many times now that there's no way to put any faith in the reliability of anything they say."

According to the affidavit filed by the detectives to obtain a search warrant, an informant named John told them that a 5-foot, 6-inch Hispanic drug dealer named Stevie was selling cocaine from the apartment.

From the beginning, a key hole in the prosecution's case has been that Lewin, who is 6-foot-2 and Jamaican, clearly does not fit that description. As a result, defense attorneys requested last year that police produce John as a witness. But the detectives said they could not find him.

Under pressure from the district attorney's office, which is investigating them for possible perjury, Detectives Carlos A. Luna, Hugo R. Amate and Paul G. Schroeder filed affidavits this week changing their story. Mark Sullivan, Luna's attorney, said the men admitted that "John" was not a real person but a composite of two informants.

Christopher Muse, attorney for Amate and Schroeder, says the detectives decided to come forward, even though they may be implicating themselves for perjury, because they "want to see justice done" in the murder of their partner.

Prosecutors say they now believe that the real informant was not John, but someone else, and that "Stevie" was merely a stock description of a typical Boston drug dealer.

Even though his case may be blown apart by the detectives' admission that they lied, O'Meara said he does not judge them harshly.

He said intense pressure from Boston's political leaders and society as a whole to crack down on drug dealers "forces good and decent young police officers into the ethical dilemma: `Should I do it right and not get it done? Or should I do it a little wrong, but get it done?' "