Murder Mystery of the Dead

The story

In the year 20XX, civilization has collapsed under a rampant zombie virus. A man in a white coat appears in a survivor community and announces, "We've discovered an antibody that will prevent zombification! He is found murdered. Attacks by "zombie believers" are on the rise all over the place. Rumors of a mysterious crazed strangler. Survivors disappear one after another, and a strange singing voice can be heard from underground every night.