For anyone still wondering how the shooter could have been activated on cue, check out the Manchurian Candidate episode of Derren Brown’s series. On YouTube for free.
In therapy, suggestive states can be induced, disassociated personalities can be created, and actions based on trigger symbols or words can be commanded and implanted. The special is also an MKUltra redpill.
MKUltra goes even further with trauma based tactics. A lot of the human brain can be “hacked” with targeted trauma and suggestion.