By 1901 the Union Pacific had run out of patience. Two train robberies in two years – one at Wilcox, Wyoming in 1899 and one at Tipton, Wyoming in 1900 – spurred them into action. Guards had been placed on trains after the Wilcox robbery but that clearly did not deter the Tipton robbers.  In January 1902, William Canada, head of the UP's Secret Service Division, hired former North Platte, Nebraska, Sheriff Timothy T. Keliher to bring together a force that would hunt down and destroy any further gangs of train robbers.

In their first year the Union Pacific Mounted Rangers, popularly known as the Bandit Hunters, were led by Arthur Grosvenor Porter, a cousin of Teddy Roosevelt. Porter left in 1903 but the Bandit Hunters carried on, led personally by Keliher. Equipped with a special train, they rode the rails from Cheyenne to the Utah line, regularly running their horses alongside the track to deter robbers. By 1905 Buffalo Bill took an interest in the Bandit Hunters, and featured them in his 1907-1909 tour of the United States.