But Cornell said yesterday that even after Malvo realized he had been manipulated and told a new version of how the shootings occurred, he continued to acknowledge that he played a role in the shootings, and that he pulled the trigger in the final sniper killing - of bus driver Conrad Johnson - and in an earlier killing in Tacoma, Wash.

The Tacoma killing was that of Keenya Cook, 21, who was shot in the face Feb. 16 last year when she opened the front door of the home of her aunt, Isa Nichols. Cornell said Malvo acknowledged shooting Cook on Muhammad's order. Nichols had worked as a bookkeeper for Muhammad's car repair business and had sided with his former wife in the couple's bitter divorce and custody fight.

"This was considered his first test to do what he needed to do - to carry out missions of violence with John Muhammad," Cornell said, adding that he believed Malvo's admission about that crime made the teen-ager's other statements to him more credible. "He told me of a crime he hadn't been charged with. That enhanced my belief that what he was telling me was the truth."

The mental health experts - six so far, including Cornell - are key to the defense's case, and whether the jury buys into their testimony is crucial to the outcome of the trial.

Today, two psychiatrists - Dr. Diane Schetky, who practices in Maine, and Dr. Neil Blumberg, who has offices in Towson and Bethesda - are expected to testify that Malvo was insane at the time of the crimes.

Yet only two months before the sniper killings began in October last year, Malvo was conflicted about the "mission," Schetky said in testimony late yesterday. She told jurors that Malvo "was in a lot of despair" in Baton Rouge, La., in the summer of 2002 while he and Muhammad were visiting Muhammad's family.

At that time, Malvo became fully aware of the plan to shoot people at random and he became "suicidal and tried to shoot himself," Schetky said. She did not elaborate.

It was not Malvo's first suicide attempt, according to the mental health expert. When Malvo was age 12 and living in Jamaica, he threatened to hang himself from a sheet because of his mother's frequent absences. Malvo's mother often beat him - a form of punishment that over the years helped drive him away from her, Schetky said.

At the same time, Malvo idealized his absent father and yearned for a substitute, Schetky said. He moved to Antigua with his mother in 2000, but she soon left for the United States, and he was left to fend for himself. He was age 15 when he met Muhammad.

"He was swept off his feet by this guy," Schetky said.

Muhammad indoctrinated Malvo in 2001 and last year with rigorous workouts, social isolation, violent movies and video games that dehumanize victims and with anti-American, anti-white dogma, the psychiatrist said. The older man also taught him that "right and wrong is perception, it's not reality," and that he needed to suppress his emotions to succeed in their mission, the psychiatrist said.

By the time of the sniper shootings, "his whole identity had merged with Mr. Muhammad," she testified. Only recently, Schetky said, has Malvo come to see Muhammad in a different light and feel used by him. She said those feelings are what prompted Malvo to recant his confessions in talks with mental health experts.

But when it comes to divining the truth, legal experts said jurors are likely to put more stock in what Malvo said on the confession tapes than what his psychologists are saying.

Christopher L. Tritico of Houston, who was one of Oklahoma City bomber Timothy McVeigh's lawyers, said recanting confessions is a tough task.

"It's like trying to push toothpaste back into the tube even after you've squeezed it out," said Tritico. "It's a real problem."