Well,Cho-Seng-Hui is still somewhat of a "mystery": He was able to make careful preperations prior the Shootings,managed to be unnoticed After he shot the two Students at the Students-Dorm Building, could send a package to NBC(is it right?),chain-shut the Doors at Norris-Hall and killed without hestitation,even shooting Victims multiple Times in Classrooms he previously went in. Planned,well-thought Behaviour on April 16th compared with his obviously delusional Manifesto and Videos,there is a huge difference between his demeanor prior the Shootings and the Moment he started his Attack. Im not a psychatrist,so i clearly dont know how to explain this properly, but i dont think he was a psychopath( especially as he "created" his Manifesto) nor a "dull" Person who just snapped. His entire Apperance on his Videos seems delusional,but he was also able to decide where to record without drawing any Attention to him. So,Psychopath,Sociopath or whatever,i guess we will never know why he did this.(Apart from his own eerie Explenations)Edit: I would find it interesting if he looked at a mirror while recording.