Legal representative's brief coordination interrupted by senior investigator (6)
I believe the answer is:
syndic
'legal representative's' is the definition.
(term for an agent or representative)
'brief coordination interrupted by senior investigator' is the wordplay.
'brief' means to remove the last letter (a shorter or briefer version of the word).
'coordination' becomes 'synch' (to synch up is to coordinate).
'interrupted by' indicates putting letters inside.
'senior investigator' becomes 'DI' (detective inspector).
'synch' with its final letter removed is 'sync'.
'sync' going around 'di' is 'SYNDIC'.
(Other definitions for syndic that I've seen before include "Government official" , "Cambridge Univ. senator" , "business agent" .)