Prosecutors gave no reason why Butler, 33, who was struggling to make a comeback, bludgeoned to death the man who was trying to help him and letting him stay in his apartment, reports The Los Angeles Times.
As his trial was scheduled to begin Butler pleaded guilty Monday to voluntary manslaughter and arson, and is to be sentenced on April 5, the report said. He reportedly suffered from bipolar disorder. He was arrested at a psychiatric center five days after the slaying and has been in custody since then.
Butler told police that Kellerman was his "only ally" in life who "went to bat" for him in troubled times, The Times report said.