Untouchable criminal can cross boundaries of agreement (10)
I believe the answer is:
sacrosanct
'untouchable' is the definition.
(both can mean infallible or unimpeachable)
'criminal can cross boundaries of agreement' is the wordplay.
'criminal' indicates anagramming the letters.
'boundaries of' means to remove the middle letters.
'agreement' with its middle removed is 'at'.
'can'+'cross'+'at'='cancrossat'
'cancrossat' is an anagram of 'SACROSANCT'.
(Other definitions for sacrosanct that I've seen before include "Too important to touch" , "Too valuable to be changed" , "Unchallengeable" , "Too valuable to touch" , "above criticism" .)