William M. Adler is the author of "The Man Who Never Died: The Life, Times and Legacy of Joe Hill, American Labor Icon."

On the morning after the killings, Salt Lake City awoke to sensational headlines. "Father and Son Slain by Masked Murderers," the Herald-Republican bannered across its front page. The father, a 47-year-old grocer named John G. Morrison, and his son Arling, 17, had been shot to death on the night of Jan. 10, 1914.

Within hours, the police had detained a prime suspect for the father's death: Frank Z. Wilson, an alias of one Magnus Olson, an ex-convict who had done time in the Utah state penitentiary. Evidence that I uncovered — in court files, clippings buried in newspaper morgues, correspondence and photographs in prison archives — shows his rampaging criminal itinerary in the days and weeks before the killings, and his startlingly violent 50-year criminal career (including a later stint as a henchman for Al Capone). Wilson was in the vicinity of the crime scene at about the time the killings happened. He not only could have killed Morrison, he also fit the profile of a potential murderer....

Hill had no criminal history. He did, however, have a fresh gunshot wound that he was assumed to have received during the commission of the crime. He had the added misfortune of looking like Frank Wilson. And police found one bit of unimpeachable evidence that made a case against Hill, although it wasn't a murder case: a red card in his pocket indicating membership in the Industrial Workers of the World, the radical labor union whose members were known as Wobblies....