Animal involved in wholesale murder (5)
I believe the answer is:
lemur
'animal' is the definition.
(lemur is a kind of animal)
'involved in wholesale murder' is the wordplay.
'involved in' indicates a hidden word.
'LEMUR' can be found hidden inside 'wholesale murder'.
(Other definitions for lemur that I've seen before include "Ring-tailed prosimian" , "Arboreal primate native to Madagascar" , "Animal with foxy face and long furry tail" , "Bushy-tailed primate" , "Madagascan monkey" .)