Each is charged with murdering six people in the county between Oct. 2 and Oct. 22 2002, including four who were shot and killed within a three-hour span Oct. 3.
Prosecutors say if convicted, Muhammad could get death while Malvo, who was 17 at the time of the shootings, faces six consecutive life sentences.
Ten people died and three were wounded during the shootings that terrorized metropolitan Washington and involved police from Washington, D.C., Maryland and Virginia on a regionwide manhunt.
Montgomery residents lived the longest with the fear that spread over the region. Schools were locked down. Police held dragnets and set up roadblocks. Routine tasks such as pumping gas or cutting the grass suddenly seemed fraught with peril.
The county police department served as headquarters of the massive search with former Montgomery Police Chief Charles A. Moose (search) the public face of that investigation.
Malvo and Muhammad were arrested Oct. 24 as they slept in their car at a western Maryland highway rest stop.
The two are charged with the murders of James Martin, 55, killed Oct. 2, 2002, in Wheaton; James L. "Sonny" Buchanan, 39, killed Oct. 3 in Rockville; Premkumar A. Walekar, 54, killed Oct. 3 in Aspen Hill; Sarah Ramos, 34, killed Oct. 3 in Silver Spring; Lori Lewis-Rivera, 25, killed Oct. 3 in Kensington, and Conrad Johnson, 35, killed Oct. 22 in Silver Spring.
Malvo, 20, already is serving a life sentence in Virginia for one of the sniper shootings. Muhammad, 44, was sentenced in Virginia to death in one of the other cases. Malvo was transferred to Maryland last month. Muhammad has challenged his extradition from Virginia. Maryland has agreed to transfer the men back to Virginia after their trials.
It is "imperative" that Malvo and Muhammad be tried again after trials in Virginia — in case those convictions are overturned on appeal, Montgomery County State's Attorney Doug Gansler said.
"It's always been argued that they (Muhammad and Malvo) should be tried under a different set of laws and facts to insure the safety of the community," he said.
Prosecutors in Maryland went ahead with the indictment while Muhammad's challenge was processed in Virginia, he said.
"We wanted to make sure that didn't delay our ability to go forward," he said.
It doesn't matter whether Muhammad is held in Virginia or Maryland for now, as long as he comes to Maryland by the time the trial starts, Gansler said. The trial will be scheduled within the next 180 days unless Muhammad waives his right to a speedy trial, and his transfer will probably occur within the next two months, he said.
Gansler said his office was intimately involved in the sniper task force's investigation nearly three years ago and are ready to present their case in court.
Gansler also has disagreed with complaints that the Montgomery cases could be costly.
"Nobody's taxes are going to go up because of this case," he said last month.
The indictments Thursday mean Malvo's preliminary hearing scheduled for June 24 will not be held.