CLIFTON, Va. (AP) — Robert F. Horan Jr., who secured a murder conviction of D.C. sniper Lee Boyd Malvo during his four-decade tenure as the top prosecutor in Virginia’s largest county, died on Friday at his home. He was 90.

The cause of Horan’s death at his home in Clifton, Virginia, wasn’t immediately determined, but he had been in hospice care, his wife, Monica Horan, said on Sunday.

Horan served as Fairfax County Commonwealth’s Attorney for 40 years before retiring in 2007. He continued going into the county prosecutor’s office for years after his retirement because he loved practicing law and being a public servant, his wife said.

“He thought the community deserved to have someone who was looking after their interests, as well as the victim’s interests,” Monica Horan said. “And he felt that people who did evil things deserved to pay for the evil things they did.”

Malvo was 17 when he and John Allen Muhammad shot and killed 10 people in the Washington area over a three-week span in October 2002. Malvo was sentenced to life in prison without parole after a jury convicted him of capital murder but declined to impose the death penalty. Muhammad was executed in Virginia in 2009.

Former Prince William County Commonwealth’s Attorney Paul Ebert worked with Horan on the sniper case, with Ebert prosecuting Muhammad and Horan prosecuting Malvo.

“He was the best trial lawyer I ever saw,” Ebert told the Washington Post.