I agree that it's probably a bad crab, but I just don't know how I'm going to get it out without disturbing the rocks and corals in my tank. I've only seen it a couple of times over the course of a few years (and each time it seems to have doubled in size!). I'm not familiar with the method that you described so I'll have to do some more research.
The weird thing is, I noticed my algae blenny bump into it on one of the rare occasions that I did see the crab and it even swam right into the crab and the crab didn't act agressive or try and grab it. And another time, I noticed my cleaner shrimp actually crawl on top of it and it didn't try and attack the shrimp. So I can't be certain that it's actually killing these things or if they just died and then he ate them. Either way, I wish I could identify the specific name and more importantly figure out how to remove it from my tank...
Any other suggestions on identifying and/or removing it would be greatly appreciated.