Criminal crossing mink with a polecat (12)
I believe the answer is:
kleptomaniac
'criminal' is the definition.
(kleptomaniac is a kind of criminal)
'crossing mink with a polecat' is the wordplay.
I cannot really understand how this works, but
'a' could be 'an' and 'an' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for kleptomaniac that I've seen before include "Motiveless thief" , "Compulsive thief" , "Obsessive thief" , "A man to pickle (anag) - one with an urge to steal" .)