Kyle Butler was one of two minor characters who only appear while Arthur is searching for Dexter, in "Hello, Dexter Morgan". He is the Kyle Butler that feels Trinity's wrath.
While Arthur Mitchell was hunting down "Kyle Butler" he came across two names in a local phone book. He went to the first Kyle's, this Kyle, address and tried to break-in. Then Kyle Butler came home and saw that he was breaking into his house. Arthur tried reasoning with him but Kyle said he was calling the police. In that moment Arthur killed him to silence him.