(DeCandido's novelizations of the Anderson films)
Following the collapse of human civilization in the wake of global T-virus pandemic, Jasper seized the Department's armory, as well as all the confiscated drugs. Over the next five years, he remained sealed in the empty building previously used by the African Revival Movement, sometimes trading drugs to the remaining population in exchange for food. He dealt with the convention center gang, despite their obvious depravity, because they were "the only game in town."
Eventually, Jill Valentine arrived in Baltimore, and swiftly established herself as an enemy of the convention center gang. By reasoning with Jasper, and reminding him of the oath to protect and serve that he had made as a police officer, she convinced him to join her cause. Together, they led the 100 survivors of Baltimore in capturing the convention center.
Following this victory, Valentine planned to leave, but Jasper convinced her to stay, saying the group needed a leader who had been out in the world and could teach them to survive in it, rather than a man who had spent years locked away from it all.