On October 11, 1925, the FBI lost one of its own for the first time. Special Agent Edwin Shanahan was staking out a Chicago garage known to be used by notorious interstate car thief, Martin Durkin. He was on the case with officers from the Chicago Police Department. The officers left the stakeout so their relief could take over. In the time between officers leaving and the new ones taking their place, Durkin arrived at the garage. Shanahan moved in to confront Durkin by himself. As he approached the car, Durkin took a revolver from the front seat of the stolen car and shot Shanahan once in the chest. Shanahan died almost instantly. He was the first federal agent killed in the line of duty.
Durkin went on the run and the FBI immediately started a nationwide manhunt. He was tracked to California but had already moved on. The FBI trailing him through Arizona, New Mexico, and into Texas. He eluded them in Texas as well but agents discovered that he was on a train to Saint Louis. It was on the train just outside of Saint Louis that they finally caught up with him. Agents and cops boarded the train and arrested Durkin without incident.
Killing a federal agent was not a federal crime at the time. Durkin was removed to Illinois to stand trial. He was convicted of murder and sentenced to 35 years imprisonment. Durkin was then tried in federal court, where he received 15 additional years for violations of the Dyer Act. The Dyer Act made interstate car theft a federal crime. Durkin spent almost 20 years at the Illinois state prison and, then did another nine in federal prison. He was released in 1954 and lived another 27 years.
photo curtesy of https://www.fbi.gov/history/wall-of-honor/edwin-c-shanahan