Copper's taken in by expert put on trial (6)
I believe the answer is:
accuse
'put on trial' is the definition.
(I've seen this before)
'copper's taken in by expert' is the wordplay.
'copper's' becomes 'cus' (chemical symbol).
'taken in by' is an insertion indicator.
'expert' becomes 'ace' (ace is a kind of expert).
'cus' going within 'ace' is 'ACCUSE'.
(Other definitions for accuse that I've seen before include "Charge with a crime" , "Put on trial" , "Blame for a crime" , "Make charge against" , "Charge with, indict" .)