Grounded winger involved in three murders (3)
I believe the answer is:
emu
'grounded winger' is the definition.
(flightless bird)
'involved in three murders' is the wordplay.
'involved in' says the answer is hidden in the clue.
'EMU' can be found hidden inside 'three murders'.
(Other definitions for emu that I've seen before include "Physics unit" , "Native Australian bird" , "Ratite" , "unit of measurement" , "European project" .)