Small rectification, the victim you mentioned was Loatian, not black. Since he was drugged up he couldn't speak comprehensible. The cops in question discarded the concerns of Dahmer's black neighbor and in stead believed everything Dahmer told them. Also out of disgust of his claim that both of them were gay, they didn't want to investigate too much, because in their own words, they'll need a shower.
But you're right about the other stuff.
It took a while before Dahmer got caught because:
1) most victims were African American
2) he was a white male living in a black neighborhood
3) he was gay in a time where it was "accepted" but at the height of the AIDS pandemic and let's be fair, homosexuality still isn't accepted by large parts in the US