Could be.but can guarantee you for more experienced guys to give you an answer then would be good idea to say how old tank is,how it was cycled,live or dry rock and tank parameters,ph,temperature,nitrates etc etc.the more detail the better my friend ^_^
emerald crabs are highly unlikely to kill a fish. The scenario would be fish died on their own and crab may have cleaned up the bodies. Though they prefer algae so even that is a stretch. I’ve not had an emerald eat a dead fish in the tank before and it’s happened a few times.
Agree with above.
Emerald crabs do not have the correct claw type for “catching fish”. They will though be happy for a free meal if one presents itself.
mad to the missing crab, emeralds usually hide during the day.