The key to understand is that he was part of a dark web network named 222 that has direct connections to foreign intelligence. Elliot Rodger also dabbled with 222. That specific cult operates just like high level government ops (because if it works it works) where the participants are blackmailed to participating in murders.

Both of these acts were connected and promoted by 222. The aim is always the same, increasing the size of the slave blackmail network, showing power, profiteering off media, pushing agendas to help ensure they will continue to maintain control etc. Etc.

Vegas was similar.

No AR was used at Sandy Hook