Guilty party (7)
I believe the answer is:
culprit
'guilty party' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for culprit that I've seen before include "One perpetrating crime" , "The one to blame, guilty party" , "baddie" , "Perpetrator of a wrongdoing" , "Offender or guilty party" .)