He seems to have had a higher than average IQ. It is possible that early on in his life he understood he was mentally ill like his father(could it be simply genetic?) and managed to lived his life as a highly function mentally ill person.... All the while holding back deep seeded anger impulses by plotting acts of violence like this for decades in his mind to placate his urges. Many times serial killers claim that the literally get high off of killing. This guy may well have had the same level of inner demons. It could be that he resisted this urge to kill for so long that when it finally manifested itself?...He just went ALL out to achieve release. The fact that he planned an escape makes me think that he was getting ready to do serial killing on a grand scale. He may well have had other targets planned after this one.