The most common and most likely answer to this crossword clue is the 4 plus 5 letter word SHOW TRIAL
I've seen this crossword clue in The Guardian
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More clues leading to the result SHOW TRIAL
- How liars start to think about travesty of justice
- Initially terrified, Warhol is being treated for poor hearing
- Pilot programme, its result fixed
- Demonstrate test that guarantees conviction
- Trails off — without question a mockery of justice
- Law history curtailed – terrible mockery of justice
- Small cry of grief mostly, before oddly terminable kangaroo court, say
Buddy explains!
The straight part
We know that "that guarantees conviction" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case that guarantees conviction = show trial.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.