Who is the killer in Montana Sky?

Answer 1

The killer is Jim, one of the mercy ranch hands. His reason is that the former owner Jack Mercy was his father. Jack threw Jim and his mother out years before. So after Jim's mother died he came back to Bozeman and hired on as a ranch hand working for Jack. In the time he worked there his anger grew, then after Jack died and the three daughters were to inherit the ranch Jim's anger grew into rage and the rest is history.