Without a thought, yells scare criminal (10)
I believe the answer is:
carelessly
'without a thought' is the definition.
(I've seen this before)
'yells scare criminal' is the wordplay.
'criminal' is an anagram indicator.
'yells'+'scare'='yellsscare'
'yellsscare' is an anagram of 'CARELESSLY'.
(Other definitions for carelessly that I've seen before include "Incautiously" , "without proper attention" , "Casually" , "Without a thought" , "Without concern" .)