Fire for detaining suspect without evidence of DNA (6)

I believe the answer is:

ignite

I'm a little stuck... Click here to teach me more about this clue!

'fire' is the definition.
(I know that fire can be written as ignite)

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

Can you help me to learn more?

(Other definitions for ignite that I've seen before include "Spark off" , "Detonate" , "Catch fire; provoke" , "Swan constellation" , "'Set alight, fire up (6)'" .)

I've seen this clue in the Sydney Morning Herald.

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