Post-mortem examination for trial? (5,4)

I believe the answer is:

stiff test

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'post-mortem' is the definition.
Both the definition and answer are singular nouns.
Perhaps you can see a link between them that I don't see?

'examination for trial?' is the wordplay.
'examination' becomes 'test' (synonyms).
'for' says to put letters next to each other (I've seen this in other clues).
'trial?' becomes 'stiff' (I can't explain this - if you can you should believe this answer much more).
'test' after 'stiff' is 'STIFF TEST'.

Can you help me to learn more?

I've seen this clue in The Telegraph.

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