Cleaner shrimp eating and killing corals!

I agree, the cleaner shrimp is most likely not doing it. I would be willing to bet it is cleaning up the mess as they are dieing or being eating by others. But this being said, each animal is an individual, and it wouldn't be entirely impossible. Heck, my hippo enjoys shredding my kenya for whatever reason every now and again, and they are supposed to be reef safe, right?
Every once in a while it's also not out of the blue to have a hermit go off the deep end and pic at corals, so that could be another reason. I would also keep a close eye on the porcelain crab. Or you have a hitch hiker

 

The flame hawk should only be added with caution to a reef environment... I would try to watch that bad boy, because he is the number one culprit out of your livestock IMO... If at all possible, setup a mounted camera and focus it on a coloney... This way you can step away and fast forward when the lights are out... then again, it could be when lights are out that there getting mutilated... hum... Either way.. watch that hawk! lol

Best of Luck

 

The cleaner shrimp is only eating dead tissue. I would not suspect him to be causing the death. 20ppm of nitrates will compromise the corals' health, then added stress of being picked on by crabs can kill it. I've never heard of filter feeding crabs, they are generally active eaters.
My cleaner likes to pull food out of my anemone too, it drives me nuts. He went and pulled out a piece of silverside that was completely inside! Since then, I cover my anemone with a net until I can't see the darkness of the silverside.