This statement is based on overwhelmng anecdotal observation.
For years I collected dead dogs from the animal pound. These canines are killed by injection with barbituate.
My purpose was to collect the bones so in spite of predation worries I wasn't about to dig all those holes and then dig the bones out again.
So I simply covered them in mulch. Occasionally on bloat, body would be air exposed and the stink noticeable. I'd simply throw more mulch on.
It wasn't long before I noticed no predation. Note I got goannas. In fact the last two years I was so confident of no predaton I was doing the canine thing I foregoed the mulch and simply threw the corpses on open ground far enough away to not smell them.
Yet other corpses dying natural death... kangaroo road kill or slashed pythons were readily predated upon.
Therefore I can only conclude goannas and what other vertebrates that eat rotting flesh somehow knew the barbituated flesh was not to be eaten!