My guess: this guy was laughed at by a group of pretty blonde girls in the 7th grade. A lot. And he took it out 20 years later on these precious, innocent little girls. The creepy thing here is he seemed to linger at the school bus stop saying good bye to his own kids that day and had so precisely planned this out. This was not a spur of the moment, crime of opportunity. This one was different.
Just my opinion...
Something tells me this shooter was a major pervert. Not sure what, but my pervert radar is going off has been ever since hearing he held a grudge for 20 years( which I doubt, just points to him being a liar a perv hallmark), he targeted young girls, and his wife is speaking out favorably in his behalf.