It's a gamble to help criminal (4)
I believe the answer is:
abet
'help criminal' is the definition.
'abet' can be an answer for 'help' (I've seen this before). I am not certain of the 'criminal' bit.
'it's a gamble' is the wordplay.
'gamble' becomes 'bet' (bet is a kind of gamble).
'a'+'bet'='ABET'
'to' acts as a link.
Can you help me to learn more?
(Other definitions for abet that I've seen before include "Help to do something wrong" , "Encourage or assist (someone) to commit crime" , "Aid as in committing crime" , "Encourage (wrongdoing)" , "Aid and assist" .)