Oh it is clear a supernatural force for evil was involved. You can understand Columbine, even Aurora, but there is zero explanation for gunning down a kindergarten class, whoever was involved, assuming that is what happened.
There is actually a very good explanation for gunning down those kids.
I am not a psychiatrist and have no training except a few courses in college.
However, I have read some things by shrinks about this incident.
One possible explanation - and it is only ONE POSSIBLE explanation-
Assume that Lanza was molested by the Priest. Assume he was told that his parents knew and approved.
He could have been saving the children.
It’s hard to understand what can go on in the mind of someone like that but this is one explanation.
The Priest at that Parish was known by the Church to have severe problems. I think he was even kicked out of a seminary and notations made about his bizarre behaviour.
We don't have to assume, there are 20 dead children's bodies, buried now in 20 newly dug graves, that PROVE the matter.
If you are still questioning whether there was actually a murder, you need to get yourself back into reality.