Reading through the comments thus far it seems that several factors have been identified as potentially to blame for this crime: the gun, drugs, the young man’s environment, etc.
These may all be contributing factors (although the elites still have not come to terms with the fact that we are never going to give up our guns regardless of how many of these tragedies they exploit), but at the end of the day, there were two culprits: this young man’s free will and the Devil.
Today’s society increasingly does not take seriously the reality of Hell. That is to be expected given that increasing numbers no longer believe in God and in fact many are shifting from rejecting Him to challenging Him.
I think it was at an apparition in Germany in the 1930’s that Our Blessed Mother warned us that society was worse off than just prior to the Deluge. I always thought that that warning applied to the tyrants of that time (and indeed it did) but looking at our sex-addicted and violence-saturated culture today, I think that Our Lady’s warnings are more relevant than ever. I think at Fatima and Akita she warned that if society keeps misbehaving we are in for a chastisement of fire. Every time one of these shootings gets publicity I am reminded of the lack of publicity given to the daily, much worse abortion holocaust.