Police informer's tied up suspect (8)
I believe the answer is:
distrust
'suspect' is the definition.
('distrust' can be a synonym of 'suspect')
'police informer's tied up' is the wordplay.
'police' becomes 'dis' (detective inspectors or DIs).
'informer's' shows a homophone (sound like) (as the word would sound if spoken by an informer).
'tied up' becomes 'trussed' ('truss' can be a synonym of 'tie up').
'trussed' is a homophone of 'trust'.
'dis'+'trust'='DISTRUST'
(Other definitions for distrust that I've seen before include "Durst sit with lack of confidence?" , "Stir dust (anag.)" , "Have no faith or confidence in" , "show a lack of belief" , "Stir dust up and be suspicious" .)