No, you are not paranoid.
Emerald crabs (and any other crab including hermits) are omnivores and oportunistic feeders...they will take advantage of any food source they can get their pointy little claws on.
I have heard many horror stories concerning these crabs, and would suggest you remove them, especially if they are already suspected of jawfish homicide and you have seen aggressive behavior.
To be fair to the crabs, there appears to be many different species of crab that are sold under the name "
emerald crab"...so their is a chance you obtained one that is more aggressive then normal. Either way, get them out of the tank, asap.
Raz
