RICHMOND, Va. — Gov. Tim Kaine denied clemency Tuesday for sniper John Allen Muhammad, clearing the way for him to be executed for the attacks that terrorized the nation's capital region for three weeks in 2002.

Muhammad is set to die by injection Tuesday night at Greensville Correctional Center in Jarratt. His attorneys had asked Kaine to commute his sentence to life in prison because they say he is mentally ill. The U.S. Supreme Court turned down his final appeal.

"I find no compelling reason to set aside the sentence that was recommended by the jury and then imposed and affirmed by the courts," Kaine, who is known for carefully considering death penalty cases, said in a statement. "Accordingly, I decline to intervene."

Muhammad was sentenced to death for killing Dean Harold Meyers at a Manassas gas station during a three-week spree that left 10 dead across Maryland, Virginia and Washington, D.C.

He and his teenage accomplice, Lee Boyd Malvo, also were suspected of fatal shootings in other states, including Louisiana, Alabama and Arizona.

The motive for the shootings remains murky. Malvo said Muhammad wanted to use the plot to extort $10 million from the government to set up a camp in Canada where homeless children would be trained as terrorists. But Muhammad's ex-wife has said she believes the attacks were a smoke screen for his plan to kill her and regain custody of their three children.

For the families of those killed, the day is a long time coming.

Cheryll Witz is one of several victims' relatives who were going to watch the execution. Malvo confessed that, at Muhammad's direction, he shot her father, Jerry Taylor, on a Tucson, Ariz., golf course in March 2002.

"He basically watched my dad breathe his last breath," she said. "Why shouldn't I watch his last breath?"

The shootings terrorized the Washington region, with victims gunned down while doing everyday chores like shopping or pumping gas. People stayed indoors. Those who had to go outside weaved as they walked or bobbed their heads to make themselves less of a target.

The terror ended on Oct. 24, 2002, when police captured Muhammad and Malvo as they slept at a Maryland rest stop in a car they had outfitted so a shooter could hide in the trunk and fire through a hole in the body of the vehicle. Malvo is serving a life sentence in Virginia.

Death penalty opponents planned vigils across the state, and some were headed for Jarratt, about an hour south of Richmond, for the execution.

Beth Panilaitis, executive director of Virginians for Alternatives to the Death Penalty, said those who planned to protest understand the fear that gripped the community, and the nation, during the attacks.

"The greater metro area and the citizens of Virginia have been safe from this crime for seven years," Panilaitis said. "Incarceration has worked and life without the possibility of parole has and will continue to keep the people of Virginia safe."

Associated Press Writer Bob Lewis contributed to this report.