Originator of hateful poster on the wall prosecuted (3,2)
I believe the answer is:
had up
'prosecuted' is the definition.
I don't know anything about this answer so I cannot judge whether this works.
'originator of hateful poster on the wall' is the wordplay.
'originator of' indicates taking the first letters (I've seen 'originators of' mean this).
'poster' becomes 'ad' (short for advert).
'on the wall' becomes 'up' (I can't explain this - if you can you should give a lot more credence to this answer).
The initial letter of 'hateful' is 'h'.
'h'+'ad'+'up'='HAD UP'
Can you help me to learn more?
(Other definitions for had up that I've seen before include "being courted" , "Brought before the court" , "Called to account before a court" , "Put on trial" .)