Person enjoying liberty heartlessly imprisoning one who rescues cats? (7)

I believe the answer is:

fireman

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'person' is the definition.
(fireman is a kind of person)

I cannot understand how the rest of the clue works.

(Other definitions for fireman that I've seen before include "Locomotive stoker" , "Fighter of blaze" , "Railway driver's assistant" , "Name fir (anag.)" , "Red engine driver" .)

I've seen this clue in The Guardian.

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