(Covers information from the S.D. Perry novels)
Steve, Trapp, Karen Driver and John Andrews (Steve's best friend) all joined with the survivors of the Raccoon City S.T.A.R.S. at Barry Burton's request, and along with Rebecca Chambers, became members of the Anti-Umbrella Movement (and at the same time fugitives) after the S.T.A.R.S. organization leadership was corrupted or subverted by the Umbrella Corporation.
Steve journeyed with the others to Caliban Cove, an Umbrella facility researching into the t-virus, in the hopes of finding evidence to use against Umbrella amidst the viral outbreak that had swept the island.
What the team found however, was far worse. Dr. Nicolas Griffith, an insane expert in drug-induced behavior modification, had unleashed his latest creation; an aerosol gas that turned all exposed into Tri-squads (or "controlled" Zombies hopelessly loyal to him), and in his insane delirium, planned to unleash the gas upon the entire world, which he believed would bring about a sort of world peace.
While separated from the others, and caring for an ailing Karen, who by this time was contaminated with the t-Virus, Steve was approached by Griffith, who believed Steve to be a strong and robust "specimen" who would serve him well. And so, Griffith had the now zombified Karen disposed of, and after having Steve restrained, injected him with the serum, turning him into a Tri-squad.
Now completely under Griffith's control, Steve lured the others into Griffith's laboratory, and together with Griffith, ambushed and trapped the entire team in an airlock chamber. With Steve completely unresponsive to their pleas, hopelessly loyal to Griffith, he shot John in the lower back, though non-fatally.
As they were sent into the chamber, the team argued that Griffith's plans were demented, and Griffith himself was insane. Griffith, experiencing a fit of rage as a result, focused it on Steve and commanded him to shoot himself in the face, killing himself in front of Rebecca Chambers, with whom he had grown quite close.