A thing like this can not be blamed on the people who did it, nor on the fact that they were out bowling before they did it, nor on their parents or the guy they got the gun from. The blame for this falls on society. In Sweden we had the highest number murders preformed by mentally ill people ever in 2008. More than half of the murdered were children. Among others a man named Anders Eklund who kidnaped, then raped then killed a 10 year old girl when she was biking home from school. Another example is a polish woman who killed 2 children in their house when they were home alone, then cut up their bodies and dumped them in the trash.
It's caused by some sort of extremism or twisted personal reality that originally comes from the polarization and segregation in society. The only thing that can counteract it -Note the ONLY in that sentance- is increasing the quality of our educational systems, increased racial & social integration and a stronger community that can pick up everyone slipping away from reality; "There is no need to be religious to go to church on sunday."