Why is there a need to find out why? Killing spree is a lot like thunderbolt. It has no prediction why it struck, in the path it stuck.
If you only want to minimize risks of future murders, then don't read/watch the news. Each time a murderer has his/her face shown, she/he is glorified in even tiniest of ways (i.e. comic book villain), with a number of murders he/she committed put in front line, number of violent copycat acts will spike.
It's completely incorrect to say there is no explanation why it struck. Maybe it's true that it was impossible to predict, maybe it's true that we will never find out the cause, but can be 100% sure there is a cause.
If you only want to minimize risks of future murders, then don't read/watch the news. Each time a murderer has his/her face shown, she/he is glorified in even tiniest of ways (i.e. comic book villain), with a number of murders he/she committed put in front line, number of violent copycat acts will spike.