A necropsy is where a vet does an 'autopsy' on a dead animal in order to determine the cause of death.
Unless you had a vet accurately diagnose redleg (Aeromonas, Pseudomonas spp.) or hemorrhagic septicemia, you cannot be sure of either.
But this is a great reason why a complete quarantine is necessary when purchasing new animals.
The only time I didn't quarantine a new animal (Taricha granulosa) is when I was given one with a full vet checkup and permission to leave the country (which involves LOTS of 'being healthy' paperwork). Even then, she's still in a separate tank because she doesn't like the setup in the other tank (she's terrestrial while the others are aquatic).
(Message edited by Joan on April 19, 2007)