When Desmond discovers that the Baphomet statue is hidden in the Vannacutt Psychiatric Institute for the Criminally Insane, he and his team, including Warren, go to Ariel Wolfe's house and abduct her and Paul for Dr. Vannacutt's journal, which may help them find the Idol.
Warren and the team then travel with the captive Paul and Ariel to the Vannacutt asylum, and find Kyle and Dr. Richard Hammer already there, also looking for the Idol. After Desmond has Warren and Harue disable the facility's lockdown mechanism to stop the building from going into lockdown, Desmond decides that the group should split up to search the asylum for the chamber where the Idol is hidden.
Warren goes off alone to find the Idol. When his finds a hollow space behind a wall via his detector, he, suspecting that it is where the Baphomet Idol is hidden, tries to use a pickaxe to break through the wall. When Warren tries to contact Desmond, a ghost grabs him through the wall, tearing his stomach open and disemboweling him, then breaking his spine and grabbing him back through the wall.
After he died, Warren's soul presumably joined the other ghosts trapped in the house. However, it can also be presumed that Warren's ghost was freed from the house when Ariel removed the Baphomet Idol from the facility just hours after his death.
Warren was shown to be violent towards Paul and Ariel. He also remarked that they made "a beautiful couple" when the two comforted one another.
Harue and Warren appeared to work together several times.