ELI5: How do shows, like NatGeo's "Underworld, Inc.", find criminals to interview?

Whenever I see shows like NatGeo's "Underworld, Inc.", where criminals are interviewed for the show, I wonder how the show goes about contacting them and getting them to cooperate. These people are often not just street-level petty criminals, but rather high-level criminals who participate in trafficking and other major crimes.

1. Are these people actually criminals, or are they paid actors?

2. If they're actually criminals, how do people who want to interview them go about contacting them?

3. What prevents these shows from turning the criminals over to the cops?

4. What makes criminals trust that they'll be safe? If real criminals are actually be interviewed by channels like NatGeo, I'd expect law enforcement agencies to attempt "Hey, want to be interviewed for this cool NatGeo show?" stings.

Thanks for any replies!