Bug in police department captures assistant commissioner backtracking on answer (6)

I believe the answer is:

cicada

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

'bug' is the definition.
(I've seen this before)

I don't understand the remainder of the clue.

(Other definitions for cicada that I've seen before include "Loud chirping insect" , "Large bug" , "Chirpy insect" , "Droning insect" , "Stridulating insect" .)

I've seen this clue in the Irish Times.

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