Larry Muller was an arsonist who was solely responsible for the torching of two churches, including St. Sebastian's. He was also the one who torched Father Anthony in his own home. He used to work for Sister Montclair as a groundskeeper for the St. Sebastian Catholic School, but left on his own accord. He became disgusted with the way the Catholic Church was working and became fanatical to the point where he decided to start setting fires. His final target was St. Dominic's. The Chicago Fire Department and the Chicago Police Department caught on to his scheme and responded to the scene. As they were evacuating the church, Severide spotted Muller bolting to his van and he immediately saw Muller hold up a dead man switch. Muller set off the switch, igniting the incendiary device and killing himself in the process.