Heartless gang imprisoned by judge, one of those firing gun? (7)
I believe the answer is:
trigger
'gun?' is the definition.
(thesaurus)
'heartless gang imprisoned by judge' is the wordplay.
'heartless' means to remove the middle letters.
'imprisoned by' indicates putting letters inside.
'judge' becomes 'trier' (a judge tries a case in court).
'gang' with its middle taken out is 'gg'.
'gg' going into 'trier' is 'TRIGGER'.
'one of those firing' is the link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for trigger that I've seen before include "Gun release mechanism" , "trip" , "arm with this?" , "Set in motion - say gunfire" , "Activating device" .)