Ever since his resurrection Norman has been a lot more ruthless, so I actually could see him willing to kill Harry. Originally Norman was a greedy businessman and sorta crappy father who only went batshit insane evil because of the GG serum -- with the convenient Osborn Amnesia giving him periods of relative decency. Post-resurrection it's usually implied that he's always been a nasty bastard who just needed the serum to push him over the edge into flying on a glider and carrying pumpkin bombs in a pink sachel.