Primate involved in wholesale murder (5)
I believe the answer is:
lemur
'primate' is the definition.
(I've seen this before)
'involved in wholesale murder' is the wordplay.
'involved in' indicates the answer is hidden within the clue.
'LEMUR' can be found hidden inside 'wholesale murder'.
(Other definitions for lemur that I've seen before include "Bushy-tailed primate" , "Madagascan monkey" , "Long-tailed primate" , "Shade" , "Nocturnal primate from Madagascar" .)