7. Black Christmas (70's version)
The Plot: Bob Clark's first outing into the season of giving (the second time being A Christmas Story), one of the creepiest serial killers in film history stalks girls in a sorority house, and manages to kill them one by one, hiding in the attic, while the rest of them desperately try to figure out what's going on.
The Solution: Look in the attic. Throughout the entire movie, there are officers running in and out of the sorority building. None of them check the darkest, most isolated place in the house. They check every other room, but not the attic. After awhile, it just comes down to process of elimination. You don't even need to think that hard, since he's propped his one of his victim's plastic wrapped body against the attic window. You can find it just from looking outside. If the decorations weren't enough to tip you off, the killer runs around laughing up there. He comes down and walks around the house to kill people. No one just think "Hey, is that the attic door opening? Is that the ladder coming down? What's up with that creepy laughter?" How did any of you get into college?