Let us in, criminally, producing useful tool (7)
I believe the answer is:
utensil
'useful tool' is the definition.
(I've seen this before)
'let us in criminally' is the wordplay.
'criminally' is an anagram indicator (I've seen this in other clues).
'let'+'us'+'in'='letusin'
'letusin' anagrammed gives 'UTENSIL'.
'producing' is the link.
(Other definitions for utensil that I've seen before include "A tool for household use" , "Useful tool" , "Item, eg for kitchen" , "Can opener, for example" , "Handy kitchen tool" .)