Millions dollars

Because it's something they would've taken (at least) a part of.

That and they see it as a breach of the brotherhood that cops have, to have each others backs. Of course they're in the wrong and have a hypocritical look on that brotherhood to begin with (no snitching), but that's there to show why he goes after them both, the gangsters and other cops, they're both crooks pulling the same crap.

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I'd love to see you in the moonlight with your head thrown back and your body on fire.

The real Richie Roberts said that he wasn't treated like that by other police officers.
It was Hollywood drama. It was to go along with the b.s. storyline that the DEA and other cops were all crooks.
Irl, not one DEA agent or officer were arrested. In fact, there was a lawsuit filed by detectives and others claiming defamation of character.

You should read about the real story, not the articles where Frank Lucus was interviewed, about what really happened. Also the true documentaries tell the real facts.

This movie is so full of untruths it's almost completely fiction.
It's a good movie, it's just not true to what really happened.
It would take me way too long to list all of the exaggerations and lies.

Police turn in large sums of money all the time. I didn't by that part of the story as realistic