BARNSTABLE, Mass. — During a nearly seven-hour interrogation, a trash collector suspected in the fatal stabbing of fashion writer Christa Worthington offered eight increasingly incriminating versions of the crime, but never wavered in his claim that a friend carried out the actual murder, the lead investigator in the case testified Wednesday.

The detective said, however, that Christopher McCowen made a curious statement at the close of the interview when told investigators were convinced he was lying and had acted alone.

"He said, 'If you did it, you wouldn't tell me,'" Trooper Christopher Mason told jurors at McCowen's trial. "He said we could stay there all night. His story wouldn't change."

The 33-year-old garbage collector is charged with first-degree murder, aggravated rape and armed burglary stemming from the January 2002 slaying of Worthington, 46, in her Cape Cod home. He faces a mandatory life sentence if convicted.

In his second day on the stand, Mason recounted how McCowen, whose semen and saliva were found on the victim's body, gradually moved from saying he only had consensual sex with Worthington to admitting he had punched and kicked her when she began yelling at his friend, Jeremy Frazier.

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The trooper said that McCowen insisted he was "innocent," because it was Frazier who plunged the knife into her chest after she accused him of stealing from her.

"Yeah, I had sex with her. Yeah, I beat her ass. But it was Jeremy who stabbed her," Mason quoted McCowen as saying.

The meaning of the various accounts McCowen gave the trooper after his April 2005 arrest is one of the most hotly disputed issues at the trial, which is now entering its second week of testimony in Barnstable Superior Court.

The prosecution and the defense agree that the statement is false. Prosecutors claim McCowen lied to conceal a much worse reality: He raped, beat and murdered a woman who was a virtual stranger to him.

The defense maintains the truth is that McCowen is innocent, but had consensual sex with the victim. His lawyer has said the incriminating statements in the interview were the result of coercive police tactics applied to a man who has an IQ of 76 and under the influence of drugs.

McCowen was arrested after lab tests matched his DNA to the crime scene. He had told investigators on two previous occasions that he had no relationship with Worthington beyond picking up her trash.

After being confronted with the lab results, McCowen started what the prosecution has described as an "evolving" admission of involvement. Every version included Frazier as the initiator of the assault and the wielder of the knife.

Frazier, who the defense has described as a drug dealer, is expected to take the stand later in the trial for the prosecution. Assistant District Attorney Robert Welsh III is also expected to call as a witness a man he claims will provide an alibi for Frazier for the time of the murder.

In his direct testimony, Mason described McCowen as being lucid and eager to cooperate. He said McCowen told him at one point that he was a fan of the shows "CSI" and "NYPD Blue" and knew that he should not speak to police without a lawyer.

But he was cooperating "because he wanted to reassure me that he hadn't committed the murder," Mason recalled.