how did he kill
the 1st guy
sharehe broke into the guys apartment, placed a slight explosive hidden in a book on the bookshelf to act as a detonator and left some kind of specially made thing on the hob, the pilot light slowly melted the outer coating, he had worked out how long it would take like a fuse, the thicker the coating the longer it took, which then released the liquid centre stuff which snuffed out the pilot light allowing the place to fill with gas. the guy came home, went to bed with no smell of gas. after he fell asleep the thing melted snuffing out the flame and filling the place with highly flamable gas, the mechanic then shoots the detonator through the window, it blows up, which detonates the whole place. now when they find the body and do an autopsy it looks like an accident caused by a gas leak, the body has no other wounds, nothing in the toxicology, the guy was alive during the fire, its simply a tragic fire due to a gas leak. no one will ever know it was planned. all evidence of his gizmos went up in smoke and there is no evidence of the bullet which would of been blown up by the thing in the book leaving nothing but tiny traces of melted lead spread all round the place, too small to detect, and the bullet hole in the window doesnt matter because the windows are all blown out anyway.
one of the best hits in any movie apart from using a hammer made of the guys bathroom tiles so when they hit the guy in the head it leaves marks the same as if the guy slipped in the shower and cracked his head open ala 'killer elite' remake.