When I was 17, I read ""The Son of Sam", written about, and by the lawyer who prosecuted David Berkowitz.
To this day, scariest book I ever read. Only because I was still naive at that age, and that book taught there are seriously mentally disturbed people out there that will kill you on a whim for no other reason than something passing through their mind. For 2-3 weeks following, I would run to my car in a panic any time I had to drive at night.