Clever as first murder victim said to be (4)
I believe the answer is:
able
'clever' is the definition.
(able can mean skilled or talented)
'first murder victim said to be' is the wordplay.
'first murder victim' becomes 'Abel' (Abel was murdered by his brother Cain in the Bible).
'said to be' shows a homophone (sound like).
'abel' is a homophone of 'ABLE'.
'as' is the link.
(Other definitions for able that I've seen before include "Having the skills and qualifications required" , "Fully competent" , "See 10" , "Adept" , "Fitted" .)