AURORA, Colo. -- A man accused of shooting and killing an Aurora police officer made an unexpected plea Monday.

Brian Washington said he's not guilty by reason of insanity.

Washington is accused of killing Detective Mike Thomas last September. Investigators said Washington walked up to Thomas' personal car while he was waiting at an intersection and shot the plainclothes officer point-blank. Thomas died at the scene.

Detectives said they believe the broad-daylight attack was apparently random. Thomas was driving his personal vehicle to a training site.

"It seems that it was a random act of hatred," Gov. Bill Owens had said at Thomas' funeral. "An evil man committing an evil action toward a perfect stranger. No one could have stopped the bullet that took Mike Thomas' life. No one could have prevented this horrible act of violence. But what we can do is take up the charge of service where Mike left off. Every American should be inspired by the life of sacrifice that consumed Michael Thomas."

Aurora's police chief has called the shooting a brutal and senseless act.

Washington has been charged with eight counts, including two counts of first-degree murder.

Washington waived his right to a speedy trial Monday.