Crossword Genius

Does he kill in church? (4,8)

Ross

I believe the answer is:

mass murderer

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'church?' is the definition.
I know nothing about this answer so I can't tell whether this works.

'does he kill in' is the wordplay.
'does he' becomes 're' (I can't explain this - if you can you should believe this answer much more).
'kill' becomes 'mass murder' (mass murder is a kind of kill).
'in' means one lot of letters goes inside another.
're' inserted into 'massmurder' is 'MASS MURDERER'.

Can you help me to learn more?

I've seen this clue in The Irish Independent.
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