Okay, so Eris or Loki or some other god of mischief comes to you in a dream, and says: "Hey dude! I've got the thing for you. It's a laser pointer that immediately sets people on fire. But it's running low on batteries, so you only get to use it thrice." And no, you can not find replacement batteries, these are godly batteries that are utterly incompatible with human technology.
Sweet! You can agonizingly kill three people in a completely untraceable fashion. Who would you turn into a human torch? Why?