This crime is completely without sense.
If you read the article carefully, which was extremely difficult, you may notice a barely disguised point being put forward.
You may also notice that this and other incidents like it are icon attacking, which like 9/11, is meant to disturb peoples psychological world models. The facts as presented do not fit with any believable psychological profile, the idea of a 20 year old pain involving school girls(Rejection cop-out) is ambiguous and incongruous with the location and publicity of the crime.
Pathosexual deviants tend to value their secrecy and choose secluded locations to act out their fantasies, usually because their deviancy is disassociative, that is, their character is split and polarized into the deviant, and the normal individual marked by noticeably callow behaviour, most other deviant profiles are similar, I call it Gollumopathy.
The revenge angle doesn't fit properly, as the motive either deviant or from the wounded angle, is rather weak. Revenge is a dish best served cold, the fact that he shot them in the back of the head indicates that he was not seeking domination or revenge, he would have shot them from the front if that was the case, this also leads me to believe that he was not a psychopath.
As my personal hero is fond of saying, when you have eliminated the possible, the impossible, however improbable, must be the truth.
There is one theory that naturally comes to mind, considering the political climate, cases such as these can and will be used as an argument for spying on innocent private citizens, in fact mothers, teachers, and just about every normal person will be begging for it. Those poor families mourning for there loss, when approached by the government saying it has a surefire way to ensure that this never happens again, will back any play, no matter how ridiculous and rights encroaching or limiting it is.
However, if what they are claiming, that spying would help prevent such things from happening, were true, I myself would back it, but knowing what I know, firstly that they couldn't stop everyone, and those deviants, realizing that the government is spying on them would simply be more secretive; and secondly, I know deep down that they (The Governament) are partly if not wholly responsible for it happening in the first place, regardless of what you want to attribute to them based on which conspiracy theory you would like to subscribe to; either they greenbaumed him, or Hyperdimensional elements did it, possibly both, or they created an environment that breeds pain and dispair.
No matter how you slice it, the answer is to remove psychopathic influences and create an environment that works to nurture the human spirit and encourage normal behaviour instead of favoring capitalist psychopathic privatization and exploitation agendas at the cost of the human soul.