I read this story in the mid-late 1970's, although it may be older based on the tech.
What I can remember of it is as follows:
- It starts out as a basic murder mystery.
- The "detective" finds that there is not just a lone victim.
- Eventually he finds that homeless and others that won't be missed are all being rendered down for the chemical components.
- Possibly the raw materials are being sold, i.e. it's just a money making scheme.
- The imagery I associate with it is all very dark...
Sadly, I can't remember the ending…