Sultanate sheltering Muslim leader shoots official investigator (9)
I believe the answer is:
ombudsman
'official investigator' is the definition.
(type of public official)
'sultanate sheltering muslim leader shoots' is the wordplay.
'sultanate' becomes 'oman' (I've seen this before).
'sheltering' indicates putting letters inside.
'leader' suggests taking the first letters.
'shoots' becomes 'buds'.
The initial letter of 'muslim' is 'm'.
'm'+'buds'='mbuds'
'oman' enclosing 'mbuds' is 'OMBUDSMAN'.
(Other definitions for ombudsman that I've seen before include "Official pursuing complaints against government departments" , "Commisioner" , "Complaint investigator" , "Government appointee who investigates complaints" , "Commissioner investigating complaints by the public" .)