Sonar used in crime (5)
I believe the answer is:
arson
'crime' is the definition.
(crime of illegally starting a fire)
'sonar used' is the wordplay.
'used' indicates anagramming the letters.
'sonar' anagrammed gives 'ARSON'.
'in' is the link.
(Other definitions for arson that I've seen before include "Pyromaniac crime" , "Sonar (anag.)" , "Fire-lighting crime" , "A burning crime" , "Criminal activity" .)