Murder in institution probed by one leading police department (8)
I believe the answer is:
homicide
'murder' is the definition.
('homicide' can be a synonym of 'murder')
'institution probed by one leading police department' is the wordplay.
'institution' becomes 'home' (home is a kind of institution**).
'probed by' is an insertion indicator (I've seen this in other clues).
'one' becomes 'i' (Roman numeral).
'leading' says to put letters next to each other.
'police department' becomes 'cid' (I've seen this in other clues).
'i'+'cid'='icid'
'home' placed around 'icid' is 'HOMICIDE'.
'in' is the link.
(Other definitions for homicide that I've seen before include "Murder (mainly US)" , "The killing of one person by another" , "Murder (of one person)" , "The killing of a human (mainly US)" , "The killing of one human by another" .)