It was her supposed death and Krei's ignorance towards innovation that led Callaghan down a dark path, eventually becoming a murderous, vicious, ruthless, and uncaring man, bent on seeking revenge on the ones who wronged him, willing to kill anyone who gets in his way, even slightly. With Abigail's demise, Callaghan's morality seemed to have vanished, and his lengths to achieve vengeance had no bounds, as he continuously made attempts to kill Hiro and his other students (originally due to the fact that they were witnesses, and later as a result of them being a threat to his plans), in addition to performing acts such as rampaging through the streets, destroying parts of the city, and continuously endangering innocent lives to the point of indirectly killing his own prodigy, Tadashi, though all with no remorse.