it may well have been a satanic thing.
At the same time, there is a plausible mundane explanation that the funeral home had accepted government funds to cremate the bodies as the families either couldn't be tracked down, or couldn't pay.
In order to save money on the natural gas (quite possibly several hundred dollars worth per body, to reduce it to ash), the funeral home may have lied to the govt and said they did the cremation, but in fact didn't do it, and pocketed the money.
The corpses could have been hidden in the ceiling.