You never know what people are up to behind closed doors—but when they live right next to you and have large windows and backyards, it's easy to get a glimpse.
People shared the creepiest things they found out about their neighbors, and they didn't even have to be spies to discover these secrets.
One of my neighbors was actually caught on "To Catch a Predator"
Edit: Just called my dad to find out what the aftermath was. He got caught. He was on TV. The prosecutor didn't handle the case correctly (not sure exactly what happened), but all of the 40 people who got caught all got off scot free. He still lives in my parents' neighborhood, but nobody talks to him and they rarely see him leave his house.
A middle-aged couple in my street got drunk with my dad a few years back and for some reason told him all about how they like to f*ck wearing scuba gear.