Strangled the Duke, suppressing corruption before heartless trial (9)
I believe the answer is:
throttled
'strangled' is the definition.
('throttle' can be a synonym of 'strangle')
'the duke suppressing corruption before heartless trial' is the wordplay.
'duke' becomes 'd'.
'suppressing' means one lot of letters goes inside another.
'corruption' becomes 'rot' (I've seen this in other clues).
'before' is a charade indicator (letters next to each other).
'heartless' suggests removing the centre.
'trial' with its middle removed is 'tl'.
'the'+'d'='thed'
'rot'+'tl'='rottl'
'thed' placed around 'rottl' is 'THROTTLED'.
(Other definitions for throttled that I've seen before include "Suppressed" , "Choked" , "Strangled manually" .)