A lawyer for a sniper who terrorized the Washington, D.C., region more than 15 years ago has asked a federal appeals court for a chance to seek lighter sentence.

The 4th U.S. Circuit Court of Appeals heard arguments Tuesday in the case of Lee Boyd Malvo, who was 17 when he and an accomplice killed 10 people in 2002.

A federal judge ruled last year that Malvo is entitled to new sentencing hearings in Virginia under a U.S. Supreme Court ruling that banned mandatory life-without-parole for juveniles.

A lawyer in the state attorney general's office urged the appeals court to keep Malvo's life sentences in place. He said Malvo waived his right to appeal when he agreed to a plea deal that took the death penalty off the table.