I don't think you need a general AI for something like this. You can detect what the other person is carrying and that works good as a filter. A person carryin

I don't think you need a general AI for something like this. You can detect what the other person is carrying and that works good as a filter. A person carrying knife in a crowd or school outside of canteen doesn't make any sense by general norms. Second would be to detect the intent - now that's a much harder problem but you can whitelist few situations where the person has already stabbed someone or shown sufficient physical evidence of criminal intent.