Washington police finally arresting target involved in scandal (9)
I believe the answer is:
watergate
'scandal' is the definition.
(I've seen this before)
'washington police finally arresting target involved' is the wordplay.
'washington' becomes 'wa' (abbreviation for the US state).
'finally' indicates one should take the final letters.
'arresting' indicates putting letters inside.
'involved' is an anagram indicator (involved can mean confusing or complex).
The final letter of 'police' is 'e'.
'wa'+'e'='wae'
'target' anagrammed gives 'tergat'.
'wae' enclosing 'tergat' is 'WATERGATE'.
'in' is the link.
(Other definitions for watergate that I've seen before include "Burgled hotel" , "scandal" , "target for a 1972 break-in" , "Means of access for a current" .)