Hypnotherapy?
Look up SSSS or "S-Quads". Also known as "Silent Subliminals". We used them in major psyops in Iraq during the Gulf War. THAT is likely the mechanism used to program/code the shooter. Through his cell phone, computer, car speakers or TV. With SSSS you can target individuals, if you have a specific enough psych profile.
I believe that is what Q was referring to.