(SPOILER) L.A. Noire homicide ending?

So apparently Garrett Mason was behind it all. My question is why did all of the other suspects who were arrested seem like they did the crime. There was clear evidence (suspect running, bloody clothes, murder weapons, etc.) pointing towards the suspects and some of the suspects basically admitted to comitting the murders at the end of the cases. Im having throuble understanding all of this. Someone PLEASE help!!!