Runs with crazy idea, using rap sheets principally to identify looters (7)
I believe the answer is:
raiders
'looters' is the definition.
('raider' can be a synonym of 'looter')
'runs with crazy idea using rap sheets principally' is the wordplay.
'runs' becomes 'r' (cricket abbreviation).
'with' is a charade indicator (letters next to each other).
'crazy' indicates anagramming the letters.
'using' means one lot of letters go next to another.
'principally' indicates taking the first letters.
The initial letters of 'rap sheets' is 'rs'.
'idea' with letters rearranged gives 'aide'.
'r'+'aide'+'rs'='RAIDERS'
'to identify' acts as a link.
(Other definitions for raiders that I've seen before include "' - - of the Lost Ark'" , "Marauders" , "Attacking force" , "Marauding attackers" .)