get the goods on
get the goods on or have the goods on {v. phr.}, {slang}
To find out true and, often, bad information about; discover what is wrong with; be able to prove the guilt of.
Tell the truth, Johnny. We know who your girl is because we've got the goods on you.
The police had the goods on the burglar before he came to trial.
Compare: HAVE SOMETHING ON.
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Source: A Dictionary of American Idioms