Lee Boyd Malvo is expected to take the stand against the man who calls him "my son" as early as today, in what promises to be the most dramatic moment so far in the Montgomery County murder trial of John Allen Muhammad.

But the appearance by the 21-year-old Jamaican - who, like Muhammad, has been convicted of a sniper shooting in Virginia - will be significant in other ways, experts say.

Although a boastful Malvo admitted to sniper shootings in taped interviews with Fairfax County, Va., police after his arrest in October 2002, he never testified at his or Muhammad's murder trials in that state. His account is expected to provide a strong counterpoint to Muhammad's claim that he is being wrongly accused, legal experts say. Muhammad, 45, who has been sentenced to death in Virginia, is representing himself in the Montgomery County trial.

Malvo's testimony could also fill in gaps about the 2002 sniper shootings that terrorized the Washington area.

Observers say Malvo's testimony and willingness to face his former mentor will show how far removed he is from Muhammad's iron fist.

"I think it will be powerful in the sense that it is a dramatic confrontation," said defense lawyer Andrew Jezic, a former prosecutor and co-author of a Maryland manual on confessions.

Malvo is expected to tell jurors that Muhammad committed five of the six killings with which they are charged and for which Muhammad is on trial, a source familiar with the case confirmed. Legal experts said Malvo's testimony is not necessary to obtain a conviction but won't hurt.

This account by Malvo would match what mental health experts testified at his 2003 sniper trial that he had told them. But it is at odds with his claim to police shortly after his arrest a year earlier that he alone was the triggerman, leaving a question of which account to believe.

Dewey Cornell, a defense psychologist from Malvo's 2003 trial, said in an interview Friday that Malvo's early statements showed his pathological relationship with Muhammad but that the younger man has gone through a profound change. Confronting Muhammad - with whom he'll come face to face during cross-examination - is "momentous" for Malvo, said Cornell, who remains in contact with him.

Awaiting trial in 2002 and 2003 and since his conviction, Malvo has been in touch with friends and family from Jamaica, and pulled away from Muhammad, to whom he is not related. The process has been akin to a person being brought back from a cult, Cornell said.

"I know that he is willing and committed to tell the truth," Cornell said.

"At one time, Lee was willing to do anything, even commit murder, for John Allen Muhammad," Cornell said. Now, incarcerated for life, he has come to see his former Svengali as the man whose empty promises stole his life, he said.

"Lee is left with terrible guilt and remorse. You think you are on a noble mission, later you discover that what you did was plain murder," the University of Virginia psychologist said.

According to defense testimony at Malvo's trial, Muhammad had told the adolescent that they would build a utopian community with $10 million they would extort from the government and that their shootings would inspire a revolution that would destroy the United States.

Malvo was 15 when he fell under the sway of Muhammad. His mother had used Malvo as collateral for the forged travel documents that Muhammad sold her so she could leave Antigua for the United States.

Malvo became what one of his lawyers at his Virginia trial called a " cult of one" to the older man. He converted from Seventh-day Adventist to Islam at Muhammad's insistence, trained as a sniper in Muhammad's control, spouted anti-American sentiments learned from Muhammad and became an accomplished and brainwashed foot soldier on Muhammad's mission, his defense maintained.

When arrested Oct. 24, 2002, with Muhammad in a trash-strewn blue Chevrolet Caprice that authorities said had been transformed into a mobile sniper's lair, Malvo took credit for all the shootings.

But his credibility will be fodder for the defense. When questioned by police soon after his arrest, he bragged about his shooting prowess, snickered as he spoke of deaths and laughed as he described James L. "Sonny" Buchanan Jr.'s lawn mower continuing on the grass while the mortally wounded landscaper stumbled.

Eight months later, no longer protecting his "father," Malvo admitted to two killings - the first on Feb. 16, 2002, and the last on Oct. 22, 2002, his defense said.