Thompson moved to Ellsworth, Kansas, which was also prospering as a cattle boomtown. On August 15, 1873, Thompson's younger brother, Billy, shot and killed Sheriff Chauncey Whitney. Whitney was standing near the two Thompson brothers, who were facing off against a local police officer, John "Happy Jack" Morco, and a gambler, John Sterling. The confrontation had developed over a gambling dispute. Whitney was a friend to both brothers, and numerous witnesses confirmed that Whitney stated before he died that the shooting was accidental.