Corrupt person's confession probed by new copper in office (9)
I believe the answer is:
incumbent
'corrupt person's confession probed by new copper' is the definition.
I can't judge whether this defines the answer.
'in office' is the wordplay.
'office' becomes 'cumbent' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'in'+'cumbent'='INCUMBENT'
Can you help me to learn more?
(Other definitions for incumbent that I've seen before include "Necessary - office-holder" , "Holder of an office or post" , "Currently holding an office" , "Functionary" , "official?" .)