One kills when elite troops stray from path (8)

I believe the answer is:

assassin

'one kills' is the definition.

'when elite troops stray from path' is the wordplay.
'when' becomes 'as' (eg 'when I walked' means 'as I walked').
'elite troops' becomes 'SAS' (Special Air Service).
'stray from path' becomes 'sin'.
'as'+'sas'+'sin'='ASSASSIN'

(Other definitions for assassin that I've seen before include "Bravo!" , "Liquidator" , "Booth, for example" , "Political murderer" , "Killer of prominent person" .)

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

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