Crossword Genius

Cop following lead tips off local expert (5,4)

Ross

I believe the answer is:

guide book

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'cop following lead tips off local' is the definition.
I know nothing about this answer so I can't tell whether it can be defined by this definition.

'expert' is the wordplay.
I cannot really understand how this works, but
'expert' could be 'guide' (guide is a kind of expert) and 'guide' is found within the answer.
The remaining letters 'book' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...

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