Not guilty — meaning prisoner returned for the first time (8)
I believe the answer is:
innocent
'not guilty' is the definition.
(I know this)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for innocent that I've seen before include "Virgin" , "Pope" , "Irreproachable" , "not intending to cause offence?" , "Naive or not guilty" .)