Officer's information on armed criminal (8)
I believe the answer is:
gendarme
'officer's' is the definition.
(gendarme is a kind of officer)
'information on armed criminal' is the wordplay.
'information' becomes 'gen' (gen is a kind of information**).
'on' is an insertion indicator.
'criminal' indicates an anagram.
'armed' with letters rearranged gives 'darme'.
'gen' going inside 'darme' is 'GENDARME'.
(Other definitions for gendarme that I've seen before include "continental copper" , "policeman in Paris?" , "Foreign policeman" , "Nice policeman" , "French officer - merge DNA (anag)" .)