Could my Coral Beauty Angel be the killer?

Hi. So I have a 35 gallon tank that we've had set up for close to 30 months now. We've had a coral beauty angel fish in our tank now for some time (maybe 8 months) and added it with a few other fish we had, a clown, dottyback, royal gramma, and a neon goby that were already living in the tank/originals. We never had any problems with introducing him to the tank and he actually seemed to be little buddies with the clown in my opinion as they were always right next to each other hanging out like a mated pair. Anyway, about two months ago I noticed one of the fish missing, the next day, I thought two were missing, then on the third day I could have sworn that it was just down to the clown and angel. We thought it was so weird that they were just disappearing over night with absolutely nothing left over. I have two other tanks that are quite larger and although rare, when we have lost a fish we can always find the body, even if it's been nibbled on by other fish or crabs. So because of that we spent several days every evening searching the live rock and sump with lights and moving things in the tank looking for these guys. I spent about another week or so waiting to see if they might just be hiding before we decided to just move on and try adding another fish. We added a diamond back goby early one morning, he did great all afternoon in the tank and the following day, but the next morning he had disappeared as well? We decided there had to be something in the rocks and decided to take every single rock, etc out of the tank and try and find what ever is going on - we even broke a few of the bigger rocks in hopes of finding something... nothing. We put the tank all together again, add the two fish we still have and waited for the tank to clear up and calm down. Keep in mind this whole time we're doing regular water changes and maintenance, we even considered that it might be a disease of sorts and have spent countless hours researching. Everything seems so normal, so it's very confusing. So after about a month and a huge reno/deep clean on the tank we think that maybe the fish just died because they were old and the goby was a fluke? Two weeks after the huge clean up of the tank and after letting it settle down we went and got a clown goby to test the tank again, same thing happens, the next morning he's gone. Then the following night the original clown fish finally goes missing?! Just vanishes. Now we're down to just the angel fish, even though we had never seen him be agressive or attack another tank mate, we started thinking maybe he's the culprit behind all of this? We did a water change and added a cheap damsel two weeks ago... I thought it was over as he was alive for three days and looked excellent, eating, etc. Then the fourth morning, he's vanished as well. So we've just had the angel alone since then and have no plans of adding or "testing" the tank at anytime in the near future with anymore fish. We have an emerald crab and sally light foot crab that have been in the tank for a while and do well as well as a coral banded and cleaner shrimp and multiple sps and lps corals that have been been looking great this whole time. We're clueless and our LFS's that are very knowledgeable have been kind of stumped with this as well. We've even brought in water samples for them thinking out test kit may have gone bad, etc. We've tried a lot. Anyway, I guess what I'm wondering is does anyone think it's possible that it could be the angel fish killing and eating them or could there maybe be some sort of something (bristle worm, etc?) hiding in the rocks that's just nibbling them up overnight? Thanks so much in advance!