William K. Foster was born 1868 in Cleveland, New York. William moved to the Arizona Territory in 1906 to try his luck at copper mining in the town of Helvetia, Pima County. William worked on occasion under local U.S. Marshal B.F. Daniels and mined with his partner J.L Tremaine on land partially owned by Daniels. On March 23, 1908, William Foster was shot and stabbed during a dispute with the owner of a Mexican restaurant. His presumed attacker was also killed and William was burried the next day on orders of Marshal Daniels.

When William's borthers, James and Bertram, learned of William's death, they were sceptical of the veracity of the story. The brothers commissioned Arizona authorities to return Will's body to New York. William's earlier correspondence wrote about his life in the West as well as the health benefits of frontier life. James and Bertram were suspicious about why William was buried soon after his death as well as some of the conflicting reports they recieved. According to Marshal Daniels' account, William was drunk "every time he got a hold of any money." However, Tremaine related a different story where William was with a man named W.P. Scott who may have started the trouble which resulted in William being killed.

The case was referred by the Governor of Arizona to the distric attorney of Pima County.In a letter from May 26, 1913, Bertram recalls how he hear a story that Marshall Daniels had profited from the sale of Williams share of the mining claim. He ends the letter by expressing his continued suspicion of Daniels and Tremaine's invovlment with William's death.