He started off as Dan Smith's instructor in the field of assassination (whilst he was a member of the Seattle Self-Defense Department), before he later turned against him - after Dan was set-up by Pedro Montana, who gave Blackburn the impression that he had been betrayed by Dan. He eventually murdered Dan on a basketball court - and he and Pedro later entered the world of organ trafficking.
When the player is first introduced to Blackburn in the game, he shoots dead a prostitute in the back of a limousine - before then entering the hotel and killing virtually everyone inside who he encounters.
Having been betrayed by Pedro (who left the world of organ trafficking behind, for a new life with his family), Blackburn eventually gets revenge by murdering Pedro's family - and confronting and taunting Pedro himself about their deaths. He throws Pedro his daughter Mary's head to him, before shooting him in cold blood.
He is later found in a labatory, by a resurrected Dan (who has been resurrected and assimilated into Harman Smith) - where he has apparently taken up taxidermy on the bodies of the victims of those he has collected for organ-harvesting, as a hobby. After a stand-off with Dan, he is slain by Dan - and his body ends up in the device he used on his victims.
He also spared one of the girls initially seized for organ-trafficking, AYAME Blackburn - who was taken from the Immagration and Naturalization Service. Like Dan, she too was trained by Blackburn in assassination.