Shown to wander within prison boundaries (6)
I believe the answer is:
proven
'shown' is the definition.
(thesaurus)
'wander within prison boundaries' is the wordplay.
'wander' becomes 'rove' (synonyms).
'within' indicates putting letters inside.
'boundaries' suggests removing the centre (only the edge or boundary letters remain).
'prison' with its middle removed is 'pn'.
'rove' inserted inside 'pn' is 'PROVEN'.
'to' is the link.
(Other definitions for proven that I've seen before include "Established beyond doubt" , "Conclusively demonstrated by evidence" , "Adjective meaning demonstrated beyond doubt" , "Established with evidence" .)