Girl seen after serious crime (6)
I believe the answer is:
bigamy
'crime' is the definition.
(bigamy is a kind of crime)
'girl seen after serious' is the wordplay.
'girl' becomes 'amy'.
'seen after' is a charade indicator (letters next to each other).
'serious' becomes 'big' (I can't explain this - if you can you should give a lot more credence to this answer).
'amy' put after 'big' is 'BIGAMY'.
Can you help me to learn more?
(Other definitions for bigamy that I've seen before include "Marrying one person while married to another" , "crime, perhaps" , "Crime of marrying twice" , "Illegal marriage to more than one person" , "Crime involving marriage(s)" .)