Science fair help please ? !?

We have a science fair next week and I want to do it on psychology and forensic science (like something about serial killers ). I wanted to do it on why people do drugs but my teacher was like no you can't test that blah blah (sorta tuned out after no ). But anyway I need a question besides what make a serial killer kill . Any ideas ? Any answers before the next 3 hours are gladly appreciated .