US sniper Lee Boyd Malvo has been sentenced to life in jail for murdering six people during a spate of shootings in the Washington DC area in 2002.
Malvo was 17 at the time of the Washington killings
He has already been sentenced to life in prison in Virginia for shootings that took place there.
"I'm truly sorry, grieved and ashamed," said Malvo, 21, who pleaded guilty to the six killings last month.
Malvo had testified against his former mentor, John Allen Muhammad, thought to have masterminded the attacks.
Ten people died and three were wounded in the killing spree in the Washington area in October 2002.
Malvo's latest life sentence was imposed by a court in Maryland, for related six murders committed in the state.
Muhammad was sentenced to life in prison earlier this year after being convicted of the same murders - and had already been sentenced to death in neighbouring Virginia.
Malvo, who was a teenager at the time of the shootings, gave the prosecution extensive information about how he and Muhammad drove around in a car with a hole drilled in the back to allow them to shoot people.
Malvo is not expected to serve any time in jail in Maryland, as he was sent for trial in the state on condition that he should be returned to Virginia after sentencing.
Muhammad's accomplice (L) testified against him in the trial
Prosecutors introduced DNA and ballistics evidence to link the two to the shootings which took place over three weeks in late 2002, terrifying people in and around the US capital.
Muhammad and Malvo's Maryland victims were James Martin, 55 - the first Washington-area victim - James "Sonny" Buchanan, 39; Lori Ann Lewis-Rivera, 25; Premkumar Walekar, 54; Sarah Ramos, 34; and Conrad E Johnson, 35.
Police as far away as Washington state and the Caribbean island of Antigua have said Muhammad may be linked to shootings in their jurisdictions.
He and Malvo could still face prosecution in connection with shootings in Alabama and Louisiana.