Steal inside information to finish off crime (6)
I believe the answer is:
tiptoe
'steal' is the definition.
(thesaurus)
'inside information to finish off crime' is the wordplay.
'inside information' becomes 'tip' (I've seen this in another clue).
'finish off' says to take the final letters (I've seen 'finishes off' mean this (take the finishing letters off of the words)).
The final letter of 'crime' is 'e'.
'tip'+'to'+'e'='TIPTOE'
(Other definitions for tiptoe that I've seen before include "Creep" , "''... through the tulips'' (Tiny Tim song)" , "Move delicately" , "Walk very quietly with heels raised" , "go quietly" .)