Killed by a cooked snail (5)
I believe the answer is:
slain
'killed' is the definition.
(slaying is a kind of killing)
'a cooked snail' is the wordplay.
'a cooked' indicates an anagram (letters cooked into a new form).
'snail' with letters rearranged gives 'SLAIN'.
'by' is the link.
(Other definitions for slain that I've seen before include "Violently killed" , "Killed, murdered" , "Put to the sword" , "Slaughtered" .)