For old trick he went to prison (2-3)
I believe the answer is:
ex-con
'he went to prison' is the definition.
I know nothing about this answer so I can't judge whether it can be defined by this definition.
'for old trick' is the wordplay.
I cannot really see how this works, but
'old' could be 'ex' (prefix meaning former or onetime) and 'ex' is located in the answer.
'trick' could be 'con' (a con is a fraud or trick) and 'con' is found in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for ex-con that I've seen before include "Old lag" , "having defected from Tory party?" , "Person once inside, now outside" , "Former prisoner, in short" , "Former jailbird" .)