The most common and most likely answer to this crossword clue is the 6 letter word DACOIT
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More clues leading to the result DACOIT
Buddy explains!

The straight part
We know that "criminal" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case criminal = dacoit.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.
What does DACOIT mean?
DACOIT noun- A bandit or armed robber, especially in India, Pakistan, Myanmar, and the surrounding region.
- To commit armed robbery.