Intriguing theory. But perhaps both your assumptions in offering it, and my assumptions in doubting it (if I'm reading you correctly) need to be brought out.
First off, people who have 'special needs' are more likely to be victims rather than perps. But the category is so broad, that it encompasses some people that may get violent.
Second, if this is a special needs person who is likely to get violent, I'd offer that from my educated layman's position, they are less likely to be involved in something that entails the amount of calculation that we seem to see in this event.
Finally, I don't see how the fitness or unfitness could be defining here. Sure, there could be many special needs folks who are unfit, or at least present as unfit. But there's nothing saying that a person without special needs, even one who is fit, could present, or just appear, as unfit -- whether or not s/he did so intentionally or incidentally. And so I don't know where to go with your speculation that a past or present special needs student might be responsible.
