The important thing to remember is this. We put these animals in our tanks as scavengers, but we have a lot of scavengers. They are not limited to this behavior, and indeed many are NOT scavengers in the wild.
But we must be sure to draw a distinction between fish that died and were eaten, and fish that were perfectly healthy and caught. It is not our nature to want to think that a fish died for some reason. We are more inclined to believe they were perfectly healthy in our care and were caught. So always be sure to have an open mind on these things, or you may be chasing the wrong problem. And by all means, if you are not directly spot feeding these animals regularly, then there is a HUGE risk involved, IMO, though spot feeding may not prevent predation as well.