Discontented illegals prosecuted then released (6)
I believe the answer is:
issued
'released' is the definition.
('issue' can be a synonym of 'release')
'discontented illegals prosecuted' is the wordplay.
'discontented' suggests removing the centre (the word's contents are removed).
'prosecuted' becomes 'sued' (I've seen this before).
'illegals' with its centre taken out is 'is'.
'is'+'sued'='ISSUED'
'then' is the link.
(Other definitions for issued that I've seen before include "Placed in circulation" , "Circulated, a statement perhaps" , "released" , "Sent out or distributed" , "Put out (a publication)" .)