Criminal I've put in the nick (6)
I believe the answer is:
thieve
'nick' is the definition.
(I've seen this before)
'criminal i've put in the' is the wordplay.
'criminal' is an anagram indicator.
'put in' indicates putting letters inside.
'ive' anagrammed gives 'iev'.
'iev' going inside 'the' is 'THIEVE'.
(Other definitions for thieve that I've seen before include "Misappropriate" , "appropriate" , "Nick things" , "Steal things" , "Pilfer" .)