Perpetrator (7)
I believe the answer is:
culprit
'perpetrator' is the definition.
(I know that culprit is a type of perpetrator)
This is all the clue.
(Other definitions for culprit that I've seen before include "Offender or guilty party" , "The one to blame, guilty party" , "The person to blame, the guilty one" , "Wrongdoer" , "Perpetrator of a wrongdoing" .)