Offender sees copper record unfinished ceremony (7)
I believe the answer is:
culprit
'offender' is the definition.
(I know that culprit is a type of offender)
'copper record unfinished ceremony' is the wordplay.
'copper' becomes 'cu' (chemical symbol).
'record' becomes 'L-P' (abbreviation for long play record).
'unfinished' means to remove the last letter.
'ceremony' becomes 'rite' (rite is a kind of ceremony).
'rite' with its final letter taken off is 'rit'.
'cu'+'lp'+'rit'='CULPRIT'
'sees' acts as a link.
(Other definitions for culprit that I've seen before include "The one to blame, guilty party" , "The person to blame, the guilty one" , "Wrongdoer" , "baddie" , "The one responsible for a crime" .)