The jury in the second Washington sniper trial has found teenager Lee Boyd Malvo guilty of murder.
Malvo killed FBI analyst Linda Franklin
Malvo was convicted of killing Linda Franklin, 47, as she loaded her car outside a store in Falls Church, Virginia, on 14 October, 2002.
The 18-year-old faces a sentence of life imprisonment or the death penalty.
Last month, a jury found Malvo's companion John Allen Muhammad guilty of murder in the shooting spree in which 10 people died in October last year.
The jury recommended that Muhammad be sentenced to death.
Malvo was found guilty of capital murder and terrorism, after he and Muhammad demanded $10m from the US Government to stop the killings.
The teenager looked blank as the verdict was returned following the month-long trial in Virginia.
Malvo's defence lawyer, Michael Arif, claimed his client had been under the spell of Muhammad, whom he looked up to as a father figure.
He said, "Lee could no more separate himself from John Muhammad than you could separate yourself from your shadow on a sunny day."
The defence also argued that Malvo, who was 17-years-old at the time of the killings, was temporarily insane because Muhammad's brainwashing had made him unable to make a distinction between right and wrong.
But prosecutor Robert Horan said Malvo was as responsible as Muhammad.
Calling the pair "peas in a pod", he said both shared the blame.
"Their willingness to kill and willingness to do it for money is common to both of them," he said.
Bragged about killings
Malvo had initially claimed he was the gunman in all the shootings, but later said Muhammad shot all but the last victim.
In his confession to police, Malvo gloated about the killings, saying: "I intended to kill them all."
Malvo and Muhammad shot their victims from inside the boot of their car
He said he and Muhammad could have continued sniping, despite the massive manhunt involving the police and the FBI.
"You don't mean nothing," Malvo told a detective.
"We will shoot with you there. We shoot with you not there. We will shoot with soldiers there."
The pair were eventually caught while asleep in their car, which had been modified to allow them to shoot their victims while hidden inside the boot.