The guilty one (7)
I believe the answer is:
culprit
'the guilty one' 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 "Perpetrator of a wrongdoing" , "he should have conviction" , "The person to blame, the guilty one" , "Wrongdoer" , "The one responsible for a crime" .)