Trial began today for the 33-year-old Matthew in Fairfax, where he is charged with attempted capital murder, abduction and sexual assault in connection with a 2005 attack.
Matthew, wearing a dress shirt and yellow tie, entered his plea in a soft-spoken voice.
Matthew was charged in the long-unsolved Fairfax case last year after his arrest in connection with Graham's disappearance yielded a hit on DNA evidence.
A pool of 100 potential jurors was called for today's jury selection.