Your closest friend is the villain. Only you know. Do you expose them?

I'd anonymously tip off authorities and pretend ignorance. Best of both worlds maybe? Or worst of both. Who knows anymore.

The victims matter more than your friendship sorry

You expose them and lose your best friend. You don't expose them and you're complicit. Either way you lose. This is why philosophy is depressing.

depends on what 'villain' means lol. stealing a candy bar? protect. murder? expose. there's nuance here people

Nope. Loyalty over morals every single time. Find me someone who'd actually do this and I'll show you someone who's never had a real friend.