The most common and most likely answer to this crossword clue is the 10 letter word TERRORISTS
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Buddy explains!

The straight part
We know that "Dangerous criminals" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case dangerous criminals = terrorists.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 TERRORISTS mean?
TERRORISTS noun- A person, group, or organization that uses violent action, or the threat of violent action, to further political goals.
- An agent or partisan of the revolutionary tribunal during the Reign of Terror in France.