check overflows and even your sump. I had a pistol shrimp in my sump for almost a year. Thought he was long gone since I had not seen him in so long.
Also, if he did die he may have been blown somewhere out of sight and your clean up crew are finishing him off. check around the sides and back for that because if this is a 2nd death you may need to look at what is causing the problem before you get anything else in that tank.
do you test your water regularly?
what are the results for a test now? (ammonia, nitrates etc..)