Some more evidence: If Tom becomes sober he reveals Kusich is a liar but if he remains drunk he takes the Sheriff's side and then disappears. Probably killed to tie up a loose end. A newspaper clipping in Chapter 5 (Frank's Lair) shows the Sheriff was quick to investigate and convict someone in a murder committed by Frank (cover-up). Also, at the beginning of Chapter 5 a newspaper clipping talks about Kusich solving multiple murders committed by Frank after his death. He was probably able to solve them so quickly because he already knew about them and now that Frank was dead he could take the credit for solving them. Is there any more evidence I missed?