Maryland prosecutors say they will bring six counts of first-degree murder against the two Washington sniper suspects.
State's Attorney Douglas Gansler says they will seek the death penalty against army veteran John Allen Muhammad.
He indicated prosecutors will not seek the death penalty against his 17-year-old alleged accomplice, John Lee Malvo, but do plan to try him as an adult.
Mr Gansler said: "We don't feel the death penalty is appropriate for juveniles."
The state will be the first to bring murder charges in the string of sniper attacks that left 10 people dead and three wounded in Maryland, Virginia and Washington.
Mr Gansler announced prosecutors' plans after a meeting with prosecutors from jurisdictions where the killings took place.
"As a group, the prosecutors involved in the investigation remain united in the cause to ensure that justice is served, that these men are held accountable for the acts they allegedly committed," Mr Gansler said.
Alabama law enforcement officials have filed murder charges against the two sniper suspects and say they plan to seek the death penalty in the fatal shooting of a woman during a robbery there last month.
The two were charged in Alabama with one count each of capital murder and one count of attempted murder in the September 21 robbery that killed a woman and wounded another outside a liquor store in Montgomery.
Police Chief John Wilson said investigators believe Muhammad fired the shots and that witnesses saw him standing over the slain woman's body. On Thursday, Wilson said one person had been spotted at the scene and he suggested it was Malvo.