Malvo's demeanor during a six-hour interview in November in which he confessed to some of the sniper shootings proves police did not intimidate him into confessing, a prosecutor wrote in a legal brief released Monday.
Malvo's lawyers want the confession tossed. They argue that Malvo's lawyers were not present and that Malvo made clear to police that he did not want to talk about the shootings.
Prosecutors offered details from the interrogation that they said showed Malvo eagerly cooperated.
At one point, Malvo chuckled as he recalled the reaction of a boy he shot at and missed, authorities said.
"Evidently, Malvo found it amusing that as the errant bullet flew past the boy's head he swatted at the air as if a bee had buzzed too close," wrote Fairfax County Deputy Commonwealth's Attorney Raymond F. Morrogh.
"Malvo actually smiled and chortled as he recounted this event."
Prosecutors do not dispute that Malvo, who was 17 at the time of the Nov. 7 interrogation, asked police, "Do I get to see my attorneys?" and later said, "My attorneys told me not to say anything to the cops until they got there," before confessing.
But Morrogh argued that those statements fall well short of the clear demand for a lawyer needed to stop questioning. "At best it was an expression of some reservation in Malvo's mind that he elected to reject by waiving his rights," Morrogh wrote.
Prosecutors are portraying Malvo as a young man who knew precisely how dire his situation was and who still decided to talk to authorities in a way that even the defense says is incriminating, says CBSNews.com Legal Analyst Andrew Cohen.
Malvo and fellow suspect John Allen Muhammad, 42, have been linked to 20 shootings, including 13 deaths, in Virginia, Maryland, Alabama, Georgia, Louisiana and Washington, D.C. Both face the death penalty.
Prosecutors have said the shootings that occurred during a three-week spree in October were part of a scheme to extort $10 million from the government.
When Malvo was first arrested, in late October, he said nothing to police who tried to question him. At his initial appearance in federal court, lawyers were unsure if the Jamaica native might need an interpreter.
But when he was transferred to Virginia for prosecution on Nov. 7, he opened up to Fairfax County homicide detective June Boyle and FBI special agent Brad Garrett, who has been involved in many recent high-profile investigations.
The two offered Malvo something to eat, and he requested veggie burgers. It took about an hour to find and prepare the burgers, Morrogh wrote, and in the meantime the three engaged in small talk.
"After Malvo had eaten and the small talk was finished, he got right down to discussing the killings," Morrogh wrote. "At times during the interview, Malvo laughed or smiled. For example, he laughed as he described shooting (FBI analyst Linda Franklin) at Home Depot in the head."
Malvo signed a waiver to his Miranda rights, which guarantee the right to remain silent and the right to a lawyer, with an 'X.' Authorities say he may have feared that his signature could be used against him as a handwriting sample.
Malvo's decision to sign with an 'X' demonstrates that he "obviously felt free to decide for himself how he would respond to police questions and requests," Morrogh wrote.
Malvo's lawyers argued that a federal magistrate in Maryland had ordered Malvo's court-appointed lawyers there to represent him in any related state proceedings. Morrogh argued, though, that the Virginia case is unrelated to the federal charges Malvo faced at the time and that the magistrate exceeded his authority by issuing such an order.
Circuit Judge Jane Marum Roush is scheduled to hear arguments on the issue April 28. She will have to decide whether Malvo's statements can be used against him at trial or whether they were obtained as a result of unconstitutional actions on the part of law enforcement officials, says Cohen.