Arrest involved capturing certain people handling money (10)
I believe the answer is:
treasurers
'people handling money' is the definition.
(a treasurer controls an organisation's money)
'arrest involved capturing certain' is the wordplay.
'involved' indicates anagramming the letters (involved can mean confusing or complex).
'capturing' means one lot of letters goes inside another.
'certain' becomes 'sure' (synonyms).
'arrest' with letters rearranged gives 'trears'.
'trears' enclosing 'sure' is 'TREASURERS'.
(Other definitions for treasurers that I've seen before include "Pursers" , "Money handlers" .)