Hume had been trailing Black Bart almost from the beginning of the thief’s career. He visited the sites of all the robberies and patiently put together a valuable list of information. Witnesses in settlements near the scenes of the robberies described seeing a polite, friendly man in his fifties, about five foot eight or ten in height with brownish gray hair, a fierce gray mustache and matching goatee, carrying a bedroll (which Hume correctly inferred carried his duster, sack disguise, shotgun and loot), passing through on foot and quickly disappearing. Hume made special note of the reports by several witnesses that the man’s boots were neatly slit at the toes as if to relieve corns – small wonder, given the territory Bart covered on foot (he never traveled by horse). Hume was well aware that this figure the locals had reported was likely to be the culprit.
Hume’s major break occurred on November 3, 1883, when Bart robbed a Wells Fargo coach headed from the town of Sonora to Milton, in Calaveras County. One of the drivers fired a shot at Bart, and forced him to promptly flee. Within the nearby brush, Hume found a cache of rations and correctly assumed that the goods were the bandit's. More importantly however, a blood-stained handkerchief bearing the laundry mark "F.X.0.7" was recovered. With the assistance of his associate Harry Morse, he spent a week visiting every laundry in the Bay Area – nearly a hundred of them, to track down where the mark originated. Eventually they inquired its origin at a laundromat on Bush Street in San Francisco. The proprietor identified the F.X.0.7 handkerchief mark as that assigned to C.E. Bolton, a man who lived in a hotel on Second Street. The arrest of Black Bart was at hand.
Hume and Morse were real detectives in a time when law work, outside of the Pinkerton Agency and Wells Fargo Operations, consisted principally of forming posses, serving warrants with a gun, and preventing mobs from lynching the miscreants. Few lawmen in 1883 put their noses on the carpet and searched for clues in the manner of a Sherlock Holmes (Holmes had not yet surfaced – his first adventure was published in 1887) and not many did the legwork that ended Black Bart’s escapades.