The most common and most likely answer to this crossword clue is the 9 plus 6 letter word ATTEMPTED MURDER
I've seen this crossword clue in The Daily Telegraph
A
T
T
E
M
P
T
E
D
M
U
R
D
E
R
Buddy explains!
The straight part
We know that "it’s criminal!" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case it’s criminal! = attempted murder.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.