Jespers was a laborer in a foundry owned by Matthew Killian, working alongside his friend Luke. At some point, Luke got his arm mangled by a machine that was supposed to replace some of the workers of the foundry, and he, Jespers, and their entire crew were instantly fired by the industrialist.
Jespers managed to find a job as a train steward on the 616 between London and Cardiff, helping his friend Luke to get work on the same train. One night in 1868, Matthew Killian boarded the train on his way to a business meeting in Wales. Peter served drinks to him and Angus Wolf, recognizing his former employer from a picture seen in the newspaper.
Feeling slighted by Killian's treatment of his workers, Jespers thought up a plan. He waited for Vivian to drug Killian and lead him to her sleeping carriage, after which he lured her away with an anonymous note. Making use of Killian's drugged state, Jespers dragged him onto the roof and threw him off just as the train crossed the River Thames.
As intended, Killian did not survive his fall, and the murder was investigated by the Assassins Jacob and Evie Frye. After their investigation, they accused Peter Jespers of the crime, who immediately confessed. As soon as the 616 pulled into the next station, Jespers was taken away by the Metropolitan Police Service.