This article says ballistics linked the rifle used in the spree to the Alabama killing ... since witnesses in that slaying said Muhammad and John Lee Malvo only had a handgun, the rifle revelation suggests a third person could have been involved.

And, this article has a Wendy's employee who saw a blue Chevrolet Caprice that was parked parallel to the Ponderosa on the back lot of Wendy's. A few minutes later, he said, a burgundy car pulled alongside the Chevrolet. He saw a man get out of the burgundy car and joined the person already in the Chevy.

And, there's the witness who (apparently) gave or tried to give Muhammad an alibi for the Ashland shooting, as discussed here.