Crossword Genius

Former agent with a circular letter gets rid of the gangster by virtue of position (2,7)

Ross

I believe the answer is:

ex officio

I'm a little stuck... Click here to teach me more about this clue!

'by virtue of position' is the definition.
(I've seen this before)

'former agent with a circular letter gets rid of the gangster' is the wordplay.
I cannot quite understand how this works, but
'former' could be 'ex' and 'ex' is present in the answer.
'circular' could be 'o' (I've seen this in other clues) and 'o' is present in the answer.
'letter' could be 'o' and 'o' is located in the answer.
This may be the basis of clue (or it may be nonsense).

Can you help me to learn more?

(Other definitions for ex officio that I've seen before include "By virtue of one's status" , "By right of office" , "By virtue of one's official position, Latin phrase" .)

I've seen this clue in The Hindu.
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