Right, but if your son comes home with blood on his clothes, and his appearance shows signs of a struggle . . . as a mom, I think she would ask what happened. No? And if she did see him in such a state, well, then, they've got themselfves a witness.
He had his own apartment so I doubt his mother even saw him when he got home, especially if he got in, in the early morning hours. I think if he had blood on them, he would have gotten rid of them, plus that is the one thing we do not have. We don't have any DNA anywhere!