Man's Punishment

There have been many murders recently. However, these aren't ordinary murder cases. The culprits are obvious, but they don't remember anything except for a bloody scene, the corpse, and a weapon with fresh blood dripping from it. Intrigued by these strange occurrences, a high schooler starts investigating, in order to find a way to prevent the problem. Eventually he falls victim to the incident as well.
Can he find a solution to the plague of homicidal sleepwalkers?