Pure fellow exposed as a doctor caught in crime (5)
I believe the answer is:
simon
'pure fellow exposed' is the definition.
I can't judge whether this defines the answer.
'a doctor caught in crime' is the wordplay.
'a doctor' becomes 'mo' (medical officer).
'caught in' is an insertion indicator.
'crime' becomes 'sin'.
'mo' placed inside 'sin' is 'SIMON'.
'as' is the link.
Can you help me to learn more?
(Other definitions for simon that I've seen before include "Peter (NT)" , "Bolivar, de Montfort, Callow or Cowell?" , "Simple chap" , "he says it's a game" , "Simple pieman" .)