Express companies turned to the Pinkerton National Detective Agency in 1874 to stop the James-Younger Gang. The Chicago-based agency worked primarily against urban professional criminals as well as targeting unions and breaking strikes. The former guerrillas, supported by many old Confederates in Missouri, proved to be too much for them. One agent (Joseph Whicher) was dispatched to infiltrate Zerelda Samuel's farm and turned up dead shortly afterward, with all but his hands eaten by the hogs that freely roamed the area. Two others, Louis J. Lull and John Boyle, were sent after the Youngers; Lull was killed by two of the Youngers in a roadside gunfight on March 17, 1874, though he killed John Younger before he died (an event depicted in the film The Long Riders (1980)). Allan Pinkerton, the agency's founder and leader, took on the case as a personal vendetta. Working with old Unionists around Jesse James's family's farm, he staged a raid on the homestead on the night of January 25, 1875. An incendiary device thrown inside by the detectives exploded, killing James's young half-brother and blowing off one of James's mother's arms. Afterward, Pinkerton denied that the raid's intent was to burn the house down.
However, a 1994 book written by Robert Dyer entitled Jesse James and the Civil War in Missouri (ISBN-13: 978-0826209597) contains the following:
"In early 1991, a Jesse James researcher named Ted Yeatman found an interesting letter among the papers of the Pinkerton Detective Agency. The letter was written by Allan Pinkerton to a lawyer working for him in Liberty, Missouri, named Samuel Hardwicke. In the letter Pinkerton tells Hardwicke that when the men go to the James home to look for Jesse they should find some way to 'burn the house down.' He suggests they use some type of firebomb."
This letter illustrates just how far Pinkerton was willing to go in his vendetta against the James brothers, but the move backfired. The bloody fiasco did more than all of Edwards's columns to turn Jesse James into a sympathetic figure for much of the public. A bill that lavishly praised the James and Younger brothers and offered them amnesty was only narrowly defeated in the state legislature. Former Confederates, allowed to vote and hold office again, voted a limit on reward offers the governor could make for fugitives.