Even after resigning as city marshal, Tilghman still held a commission as a Ford County deputy sheriff. Law enforcement duties brought him to Farmer City, Kansas on his thirty-fourth birthday – July 4, 1888 – where he shot and killed a man named Ed Prather. The local paper reported that Prather "made frequent threats against Wm. Tilghman, the deputy sheriff, who took all the abuse from the excited man without offering any retaliation ... in conversation with Mr. Tilghman, he became very abusive and threatened to put an end to him right there, and suiting action to his words, he threw his hand upon his revolver; but Mr. Tilghman was too quick for him and held a revolver in his face. Mr. T. ordered him three times to take his hand off his gun, and would have disarmed him if he had been near enough; but Prather sought a better position, but Tilghman pulled the trigger and Prather was a dead man. A coroner's jury ... after a thorough examination of the circumstances, returned a verdict of justifiable killing."