Had a bit of an algae problem develop so this past weekend I did thorough scrub down in the tank, moving objects and checked everywhere. Took both filters apart (AC70 x2) searched around the tank and stand ... no stone left unturned so to speak. The pleco is gone. I don't believe the syno ate it, I think he just killed it once again. The others I figured cleaned up the carcass either the senegal bichir or african butterfly cichlids. I very much doubt my bichir killed it, he won't eat live food anymore. I had up to 20 ghost shrimp with him at one point ... it was the addition of my 2 butterfly cichlids that started cleaning them up, plus the 3 cherry barbs and 2 platy's he hasn't eaten in 2 months. He wouldn't even eat the fry from the Platy's that were in the tank.
We left for 4 days at the end of June start of July. It was the last time I saw the pleco, haven't seen him since we got back. Then last week started to notice algae on all my tank walls .... so I cleaned the whole tank and searched. That's how I know he's gone, and not hiding. I've had the syno for 4 yrs now and its only plecos he kills, so far 4 to be precise. Wish I knew just how old it is ... it might explain its temperament.