...do not hastily bring into court, for what will you do in the end, when your neighbor puts you to shame? Argue your case with your neighbor himself, and do not reveal another's secret...
Proverbs 25:8-9 ESV

Even if you see someone do something wrong with your own eyes, don't rush to judgment if it doesn't seem in character. There are always circumstances that you can't see. Go to him and ask for an explanation. If it's something innocuous, leave it at that without discussing it further with him or anyone else. If it's something shameful, but not criminal, still keep it to yourself.