It is clear to me that Gangster Frank Seymon, (more with the animal masks) (Ed Note- Ray may have been wearing a kevlar vest)

killed both his business partner Casper and Detective Ray Velcoro, unclear  why he killed Casper (maybe Casper was blackmailing him and the revelation is worse than losing $10 Million) but after working Ray for years he knew he was most likely to follow the twisted, really twisted trail back to Seymon. He could see the entire field.