According to the second game, Resident Evil 2, he injected himself just to protect his life after soldiers from the U.S.F.U. (Umbrella's Special Forces Unit) shoot him for not giving away the G-Virus.
He injected. This was according to the second game. Himself just to protect his life after soldiers from the U.S.F.U.. (Umbrella's Special Forces Unit) shoot him the U.S.F.U. for not giving away the G-Virus. The second game was Resident Evil 2.