Evidence against Dahmer...
First off, Dahmer had decomposing bodies in his apartment. He had three human heads and Human meat in the freezer. Hands from several of his victims and a penis were found in a closet. Two skulls that were painted grey were found in his closet. Male genetals were preserved in Formaldehyde. A bottle of Chloroform was found which investigators found out that it was used to drug the victims. They also found hundreds of photos of the victims before, during the murders, and after death. All of this evidence was eventually used in court.