Cunninghams staying qualities were finally rewarded after Black Barts holdup of the stage from Sonora to Milton on November 3, 1883. Arriving at the point where the stage was robbed, the sheriff examined the ground very closely. Suddenly he reached down and picked up a handkerchief, which incident marked the end of Barts career. Cunningham examined the handkerchief very closely and the officers who were with him eagerly waited to see what he would say. At last we have a clew, he said and directed his associates attention to the laundry mark FX07.
The handkerchief was taken to San Francisco and after a long search similar marks were found on other linen in a laundry, by Harry Morse, head of the Morse Patrol and Detective Agency of San Francisco. While Morse was in the office of the laundry investigating the marks on the handkerchief, he was told by the proprietor that the gentleman who owned that particular handkerchief was a respected customer, having mining interests in California, and he occasionally called at the laundry. By a rather remarkable coincidence, the owner of the linen walked into the building while Morse was there and the detective immediately engaged him in a conversation by stating he understood he was interested in mines. Incidentally Morse told him he had some property he would like to submit for his consideration and that he would be glad to show him sample of ore as well as give him other details of the mining prospect. Bart apparently fell for what his newly made acquaintance had to offer and agreed to accompany him to the latters office on Montgomery street. When Bart entered and took in the surroundings, he was satisfied he had been trapped for he threw up his hands and exclaimed, Gentlemen, I pass.
That was the end of Black Barts career in stage robbery and it was brought about by the handkerchief which Sheriff Cunningham found. This sheriff served his county nearly twenty-seven years and died in 1900 with a splendid record for bravery and uncompromising honesty.
Black Bart was a person of great endurance, a thorough mountaineer, who was probably unexcelled in making quick transit over mountains and steep grades. He was comparatively well educated, a general reader and well informed on current topics. He was cool, self-contained, with humorous tendencies, and after his arrest exhibited genuine wit under most trying circumstances. He was neat and tidy in his dress, highly respectable in appearance, polite in behavior, rather chaste in his language, never used profanity, and was not known to have gambled or to have bought pools in races, or every having dealt in mining stocks. He was a Civil War veteran, having been affiliated with Company B, 116th Illinois Infantry. He pleaded guilty to the charge of stage robbery, was taken to San Quentin prison on November 21, 1883, and discharged therefrom on January 22, 1888. A short time after his release he disappeared and was never heard from again.