Ask the mad criminal for final impression (5,4)
I believe the answer is:
death mask
'final impression' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Maybe you can see an association between them that I can't see?
'ask the mad criminal' is the wordplay.
'criminal' indicates an anagram.
'ask'+'the'+'mad'='askthemad'
'askthemad' with letters rearranged gives 'DEATH-MASK'.
'for' is the link.
Can you help me to learn more?
(Another definition for death mask that I've seen is " Image of deceased taken in face cast".)