Prime Suspect claimed ID left unused (4)
I believe the answer is:
acme
'prime' is the definition.
(thesaurus)
I don't understand the rest of the clue.
(Other definitions for acme that I've seen before include "Zenith - optimum" , "crown" , "Point of maximum development" , "Highest point of excellence or achievement" , "'Highest point, apex (4)'" .)