Trained killer helping to make bureaucrat terrified (6)

I believe the answer is:

ratter

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'trained killer' is the definition.
The definition and answer can be both animals as well as being singular nouns.
Maybe they are linked in a way I don't understand?

'helping to make bureaucrat terrified' is the wordplay.
'helping to make' indicates a hidden word.
'RATTER' is hidden within 'bureaucrat terrified'.

Can you help me to learn more?

(Another definition for ratter that I've seen is " Rodent-hunting dog".)

I've seen this clue in The Independent.

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