Crime of a clergyman who's lost his head? (5)

I believe the answer is:

arson

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'crime' is the definition.
(crime of illegally starting a fire)

I cannot understand how the rest of the clue works.

(Other definitions for arson that I've seen before include "Pyromaniac crime" , "Sonar (anag.)" , "Act of a pyromaniac" , "Criminal activity" , "Criminal pyromania" .)

I've seen this clue in the Evening Standard.

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