Criminal child - he's asleep (9)
I believe the answer is:
kidnapper
'criminal' is the definition.
(I know that criminal can be written as kidnapper)
'child he's asleep' is the wordplay.
'child' becomes 'kid' (synonyms).
'he's asleep' becomes 'napper' (I can't justify this - if you can you should give a lot more credence to this answer).
'kid'+'napper'='KIDNAPPER'
Can you help me to learn more?
(Other definitions for kidnapper that I've seen before include "Captor of a human being, for ransom" , "One may take issue" , "serious offender" , "Captive abductor" , "One wrongly takes" .)