Videoconferencing technology, akin to that used in closed-circuit television, allows a witness in a distant location to be questioned by lawyers in the courtroom, with the jury watching the responses on a large screen.
The decision by Fairfax County Circuit Judge Jane Marum Roush means that Malvo's lawyers will have to try to get government permission for his mother, Una James, to re-enter the country to testify in the capital murder trial.
James was deported in November to Jamaica, having arrived in the United States in 2000 from Antigua with fake travel documents that she bought from Malvo's co-defendant, John Allen Muhammad, 42.
"We will have to pursue other options to try to get her into the country," Petrovich said.
He would not elaborate. Petrovich described her testimony as "critical" to the defense of the 18-year-old.
Malvo was James' collateral for travel papers. She gave him to Muhammad, promising to send payment for the papers once she was in the United States, said John Fuller, an Antiguan lawyer who investigated Muhammad and Malvo's activities on the Caribbean island for the attorney general there.
More than a year later, and after what was alleged to be a sham marriage she hoped would keep her in the United States, she went to Bellingham, Wash., where Malvo and Muhammad were living in a shelter. She briefly was able to reclaim her son, but after police realized she was in the United States illegally, she and Malvo were turned over to immigration officials.
Petrovich said he believes it's important for any 18-year-old in Malvo's situation to have his mother present.
Malvo's defense lawyers said they will start to make arrangements to bring witnesses from the Caribbean, Louisiana and Washington state to Chesapeake, Va., where Malvo's trial is scheduled to begin Nov. 10.
They contended that video conferencing would save more than $11,000 in expenses while giving prosecutors the ability to cross-examine distant witnesses and letting the jury see them.
"We are unwilling to make this trial a test case for this technology," Raymond F. Morrogh, chief deputy commonwealth's attorney for Fairfax County, said outside the courtroom.
The dynamics of a courtroom -- its decorum, its gravity, a witness' demeanor -- work to create a greater likelihood of telling the truth, Morrogh said.
Asked about Malvo's mother, he said prosecutors would like to cross-examine her in person.
Malvo faces the possibility of execution if convicted of capital murder in the fatal shooting last October of FBI analyst Linda Franklin near Falls Church.
Also yesterday, jury selection entered its third day in the Muhammad trial in Virginia Beach, Va. The judge hearing the case said he was committed to seating a jury by the end of today, even if it means staying later than expected.
The panel will have 12 jurors and three alternates, but the court first must find a qualified pool of 27 people. That pool will be narrowed to those needed for trial. Twenty qualified jurors have been approved.
"I'm committed to get this jury selected by [today], one way or another," Judge LeRoy F. Millette Jr. said. Opening statements are expected Monday.
Muhammad appeared to be in better spirits yesterday than earlier this week. At times he spoke animatedly with his lawyers and once applauded with the lawyers and court gallery when the judge announced that three clerks in the courtroom received news that they had passed the bar exam.
Most of the time was spent on individual questioning of jurors on topics such as their views on the death penalty and the fear they felt during the sniper shootings. Several people were dismissed because they said they had moral objections to the death penalty and could not vote to impose it.
Defense attorneys fought to keep one woman who said the state doesn't have a right to take a human life under any circumstances. "We think the defendant has a right to have people of all views sit on the jury," said lawyer Jonathan Shapiro.
But Millette said: "The commonwealth is entitled to have jurors who can weigh both possible penalties" -- death or life in prison without parole.
Others were dismissed because they said they believed Muhammad was guilty. Nine of the 16 jurors questioned yesterday were dismissed.
Muhammad is charged with two counts of capital murder in the death of Dean H. Meyers, 53, at a Manassas, Va., gas station. His trial was moved to Virginia Beach to find jurors who didn't feel threatened by the shootings.