Who do I think did it?

I think that the cocaine loving serial killer William Mansfield is responsible. He was spotted there the day of the murder, and he has a similar style to the Villisca Murders.

I feel that Reverend Lyn Kelly was at the wrong place at the wrong time. I believe that he either was a peeping Tom and saw the murders happen, or when he got on the train to leave, William Mansfield may have gotten onto that same train. If they were to have a conversation about the incident, Rev. Lyn Kelly could have continued to talk - passing along the word to other travelers. I do believe that Rev. Lyn Kelly is a little unstable mentally, but I don't think that he committed the murders.

I also think that Mansfield may have found the spare key, let himself inside, and hid in the closet until everyone was asleep. After the murders, he must've put the key back somewhere and fled.