He finds criminals working for the police (9)
I believe the answer is:
detective
'he finds criminals working for the police' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'he' is the wordplay.
I cannot quite see how this works, but
'he' could be 'ive' and 'ive' is located in the answer.
The remaining letters 'detect' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for detective that I've seen before include "police officer" , "Expert solver of clues" , "Policeman, say" , "Private or police investigator" , "Criminal investigator" .)