First killer mentioned as crook (4)
I believe the answer is:
cane
'crook' is the definition.
(thesaurus)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for cane that I've seen before include "Eg, rattan" , "Beat; sugar producer" , "Hollow jointed stem of, say, bamboo (4)" , "African country formerly called Gold Coast" , "Rod for beating" .)