He is found mortally wounded laying in front of a storage silo east of the Police Station entrance, and gives the Hero the side quest Last Will, in which the Hero must deliver his last will and testament to his family. The Hero will find his brother, Raymond, inside Saint Christopher's Church.
Barker does not actually die during the quest, as he can be found still breathing if the Hero revisits him before delivering the will to his brother. Once the Hero delivers the will and completes the quest, Barker's body will disappear. Indicating that he probably turned into a Zombie.