Sonar involved in crime (5)
I believe the answer is:
arson
'crime' is the definition.
(crime of illegally starting a fire)
'sonar involved' is the wordplay.
'involved' indicates an anagram (involved can mean confusing or complex).
'sonar' is an anagram of 'ARSON'.
'in' acts as a link.
(Other definitions for arson that I've seen before include "major crime" , "It may get you in court" , "Criminal pyromania" , "Malicious fire-raising" , "serious offence" .)