Arson involved echolocation (5)
I believe the answer is:
sonar
'echolocation' is the definition.
(I've seen this in another clue)
'arson involved' is the wordplay.
'involved' indicates anagramming the letters (involved can mean confusing or complex).
'arson' is an anagram of 'SONAR'.
(Other definitions for sonar that I've seen before include "Detection system at sea" , "Means of detecting" , "Echo-sounding device" , "System to locate underwater objects" , "Underwater detection device" .)