Crossword Genius

Sniper woman admitting to murder alongside car (11)

Ross

I believe the answer is:

bushwhacker

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'sniper' is the definition.
The definition and answer can be both people as well as being singular nouns.
Perhaps there's an association between them I don't understand?

I don't understand how the remainder of the clue works.

Can you help me to learn more?

I've seen this clue in The Sunday Times and The Times.
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