I don't think it's Matt. I don't think it's Christian either. He was too upset talking to the fake victim imho. I think the writers are using this twist to introduce some info on Christian's past. When they show them finding all these clues at Christian's it makes me think the cop is setting him up. She probably has a key or something from when they were all 'dating' and she seemed to really be into Kimber. Things are still pointing to the new doctor however that is a pretty obvious leap sooooo it's still up in the air for me .
Matt is really getting on my LAST nerve. Last night when he acted like he was so above hitting Sean I wished Sean would have grabbed something and hurled it at him lol.