The most common and most likely answer to this crossword clue is the 13 letter word SAFE-CRACKERS
I've seen this crossword clue in The Guardian
S
A
F
E
-
C
R
A
C
K
E
R
S
Buddy explains!
The straight part
We know that "criminals" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case criminals = safe-crackers.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 SAFE-CRACKERS mean?
SAFE-CRACKERS noun- One who breaks into safes.