"If society's ultimate penalty should be reserved for the most heinous offenses, accompanied by proof of vileness or future dangerousness, then surely this case qualifies," Justice Donald Lemons wrote.
Muhammad was convicteober 2002.
Lawyers for Muhammad argued on appeal that Muhammad could not be sentenced to death under state law because, they said, he was not the triggerman in the shooting spree.
They also claimed that an anti-terrorism law that was the basis for one of the capital murder counts is unconstitutional. The law had been passed in the wake of the Sept. 11 attacks. The court heard arguments in the case Nov. 2.
"I've had my fingers crossed all these months," said Prince William County Commonwealth's Attorney Paul Ebert, who prosecuted Muhammad. "Now I can uncross them."
The Supreme Court unanimously upheld the conviction based on the anti-terrorism law but split 4-3 in affirming the conviction under the triggerman rule.
The court's majority found that even if Muhammad's accomplice, Lee Boyd Malvo (search), pulled the trigger, Muhammad was eligible for the death penalty as an "immediate perpetrator" of slaying.
"Muhammad, with his sniper team partner, Malvo, randomly selected innocent victims," Lemons wrote. "With calculation, extensive planning, premeditation and ruthless disregard for life, Muhammad carried out his cruel scheme of terror."
The dissenting justices said Muhammad's actions — positioning the sniper team's car and telling Malvo when to fire — "were of the same character as those of a lookout or wheelman in a robbery."
The court found no constitutional flaw in the anti-terrorism law, rejecting Muhammad's claim that "intimidation" and other terms should have been defined in the statute. Muhammad's lawyers also had argued that the law was improperly used against Malvo because it was intended to address terrorism like the Sept. 11, 2001, attacks.
"Nothing in the words of these statutes evinces an intent to limit its application to criminal actors with political motives," the court said.
Defense lawyers also claimed on appeal that prosecutors improperly offered conflicting theories in the trials of Muhammad and Malvo.
Muhammad's prosecutors portrayed him as a manipulator who molded his then-17-year-old cohort into a killer, the defense attorneys said, while Malvo's prosecutors — seeking to counter Malvo's insanity defense — described the teenager as a willful, independent thinker who was free of the older man's influence.
"A successful rebuttal of Malvo's affirmative defense of insanity is not inconsistent with a theory of prosecution that includes Muhammad engaged in training and directing Malvo in their sniper team activity," Lemons wrote.
Malvo is serving life in prison without parole for the slayings of Philadelphia businessman Kenneth Bridges and FBI analyst Linda Franklin.