Most probably it's no. 3. I saw my hermit crab limbs lying on the ground one day but it was just walking around near to it. But you still probably have a mantis/pistol in your tank, just that it hasn't killed your hermit.. yet..
Ahaha my 3inch mantis has escaped into my main tank countless times. usually I just put some food at the top and he will come swimming out and I just net him.. quite easy
actually yesterday I camped at the tank for hours with a camera and a camel shrimp inside! and the bugger didn't even attempt to attack the shrimp. I asked Henry after that and he said it was probably because the mantis is going to molt soon so he won't whack anything