In a legal brief made public Tuesday, Fairfax County prosecutor Raymond Morrogh also said Malvo made multiple confessions to the Oct. 14 shooting of FBI analyst Linda Franklin, the case that is expected to be his first to go to trial.
The brief was the first official confirmation of reports from anonymous sources that Malvo had confessed to taking part in the multistate shooting spree last year that left 13 people dead and six wounded. It also was prosecutors' first substantial description of the relationship between Muhammad, 42, and Malvo, 18.
The pair "acted as a unit," Morrogh said. "One would be the spotter, while the other would do the shooting."
Malvo also "claimed both were equals and either could call a particular shot on or off," Morrogh wrote.
Nothing in the brief indicates that prosecutors have any evidence that Muhammad fired any shots. But if the pair acted as a team, Muhammad could get the death penalty under Virginia's new anti-terrorism law, passed in the wake of Sept. 11.
Malvo's confessions are unusually detailed and are corroborated by other evidence, Morrogh wrote. He added that Malvo has expressed no remorse.
Morrogh wrote that the confession made by Malvo "was uncoerced and completely voluntary. ... In fact, the Defendant was calm and rather boastful of his doings in this case."
The two men have been accused of shooting 19 people, killing 13 and wounding six in Alabama, Georgia, Louisiana, Maryland, Virginia and Washington, D.C. No one was hit in another incident, in which a bullet went through a craft store window.
Malvo is set for trial in November in the slaying of Franklin. Muhammad is scheduled for an October trial in another slaying in neighboring Prince William County. Both face the death penalty.
Morrogh's brief was a response to a request from Malvo's lawyer, Michael Arif, for any evidence that might clear his client. "The Commonwealth does not have evidence that casts doubt upon Defendant's guilt," Morrogh wrote.
Efforts to reach Arif Tuesday evening were not immediately successful. Peter Greenspun, who represents Muhammad, was out of town Tuesday and could not be reached for comment.
Also Tuesday, Fairfax County Commonwealth's Attorney Robert F. Horan Jr. said he still had not decided whether to seek the death penalty against Malvo because he had not yet seen all the evidence in the case.
"If at the end we feel there's sufficient evidence to ask for the death penalty, we will," Horan said.