Will We Always Know if a Criminal Has been Using Marijuana?

Last Sunday I suggested the likelihood that Axel Rudakubana, the Southport mass killer had become insane after using matrijauna, probably at school. I couidl nto state it as a fact, because I did nto nd do not know it to be. I thought and think it likely because TRudakubana's personaliyy chnaged dramatically around the age of 12, a common experience amomng children who are introduced to marijauna in Britain's chools. This tends to happen round the age of 11, when secondary school begins,  though...