The most common and most likely answer to this crossword clue is the 6 plus 3 letter word INSIDE JOB
I've seen this crossword clue in The Times
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More clues leading to the result INSIDE JOB
- Criminal act, one perpetrated in prison?
- Jailed by judge, ex-pupil’s assisted crime
- Type of crime where Jacob keeps account?
- Type of crime committed by a prisoner?
- Perfidious crime, as air conditioning is for Jacob?
- Crime committed with collusion of jailed piece of work
- Doing time post criminal activity
- Undercover work?
- Locked up unlucky chap for act of treachery
- Patience found here, perhaps, in work of fifth column …
Buddy explains!

The straight part
We know that "Type of crime" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case type of crime = inside job.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.