CHESAPEAKE, Va. - Offering a sinister description of the teen-age half of an alleged killing team, a Virginia prosecutor told jurors yesterday that Lee Boyd Malvo knew exactly what he was doing when he gunned down one victim after another in last fall's murderous rampage.

"They didn't just willy-nilly go to places and shoot," Fairfax County Commonwealth's Attorney Robert F. Horan Jr. said in opening statements of Malvo's trial. "There is no way in the world he doesn't know what he did, how he did it and why he did it."

The six- to nine-week trial will offer the public its first look at some of the evidence against the Jamaican-born Malvo, who authorities believe pulled the trigger in most of the shootings.

Jurors will hear Malvo's confession to a Fairfax County detective and FBI agent, in which they say he bragged - sometimes with laughter - about several killings.

Prosecutors say Malvo snickered at how James L. "Sonny" Buchanan Jr.'s lawnmower kept going while the mortally wounded man stumbled off after being shot Oct. 3, 2002, in Montgomery County. They say Malvo also talked of how satisfied he was with his own precision aim from more than 150 feet that sent a bullet tearing off part of Linda Franklin's head.

Horan outlined 12 shootings to be introduced by prosecutors at the trial. He pooh-poohed the insanity defense Malvo is pursuing: "The defense, in short, will be based on the hypotheticals of the mental health crowd."

After Horan's hour-long remarks, the defense countered by tugging at the heartstrings of the nine-woman, seven-man jury panel, describing Malvo as an uprooted child so desperate for adult attention that he was easy prey for the cult-like domination of John Allen Muhammad.

Malvo's lawyers are claiming that Muhammad took a slight, bullied adolescent, routinely abandoned by his mother in Jamaica and Antigua, and turned him into a killer.

They told the jury that Muhammad used extreme video games, books and audiotapes to train him, at one point even chaining him to a tree in the bitter cold of Washington state to toughen him.

"John Muhammad changed him, he indoctrinated, he made him his child soldier," Craig S. Cooley, one of Malvo's court-appointed lawyers, said in an opening statement that lasted nearly two hours.

Cooley said Malvo's mother had a "save the eye" philosophy of child rearing, telling people with whom she left her son to do whatever they had to do to keep him in line - short of putting out his eyes.

It made Malvo, whose parents split when he was about 5 1/2 , exceedingly obedient to the people with whom his mother deposited him for months at a time, Cooley said. Clearly seeking sympathy for his client, Cooley projected photos of Malvo as a child - in an oversized pumpkin-colored suit, as a babe in arms - and said Malvo was so despondent about his mother's absences that he threatened to kill himself. After he calmed down, she beat him, Cooley said.

Then she took him to Antigua, where she enrolled him in school and left again - this time on fake travel documents she purchased from Muhammad, defense attorneys said.

Once more abandoned, Malvo turned to Muhammad, who had spirited his children away from his estranged wife and was living in a stilt house with another family, Cooley said. Malvo was 15 at the time - and was ripe for doing everything the father-like Muhammad demanded, the lawyer said.

Malvo's trial is recessed until Monday, when Horan will begin presenting the prosecution's case. The delay is the result of evidence that a jury needs as it deliberates in the Muhammad trial in Virginia Beach.

Malvo's trial was moved from Fairfax County, where he is charged with killing Franklin, a 47-year-old FBI analyst, on Oct. 14, 2002, in a Home Depot parking lot near one of the wealthy county's busiest intersections.

He is charged with two counts of capital murder. One accuses him of carrying out multiple killings in less than three years. The other is under Virginia's untested anti-terrorism law, claiming that the killings were an effort to extort $10 million from the government.

But Cooley said the motive was something else entirely. He said Muhammad, bitter from failed marriages, loss of his children, failed businesses, problems in the Army, and blaming American society as racist, converted to his own brand of Islam and - with 140 children collected from around the world - vowed to build a utopian society in Canada.

Cooley also said Muhammad wanted to recover his children from his ex-wife, who moved to Clinton, Md., to escape him. The shootings were an ever-widening circle around Clinton, and Cooley said Muhammad probably was figuring on killing Mildred Muhammad and stepping in to reclaim his motherless children.