What's your evidence that he is a psychopath other than that he killed a whole bunch of people? Was he humiliated and abused as a child?
Psychopathy is more commonly associated with serial killers, not mass-murderers, by the way.
Because if the guy was insane, he would be disfunctional and would not be competent enough to have been a candidate for a PHD in neuroscience. Insane people cannot function in society to such a degree, but psychopaths surely can. Because they know what they are doing.
As for him being abused as a child? I don't know, do you? Plenty of people have had rough childhoods, but that does not make them monsters. I am guessing we will learn more about the guy's past as time rolls on, but he was far too functional and smart of an individual to fit the classification of someone who is insane. He sure as hell fits the profile of a cold and calculating psychopath who felt he had an axe to grind, though.