When a California group home for troubled children collapsed in June 2013 amid allegations that an 11-year-old had been raped, much of the backstory was a mystery.

Taking on the formidable task of unraveling that story, ProPublica’s Joaquin Sapien spent months building relationships with former staff members, he tells editor Joe Sexton in today’s podcast. “It was just a process of gaining each individual person’s trust,” he says.

In what Sexton calls “a pretty remarkable reporting coup,” he even persuaded the home’s administrator to go on the record with her experience.

When the story published last week, many of Sapien’s sources reached out to thank him for his reporting – but one call had a particularly powerful effect on him.

Hear more in the full podcast, available on iTunes, SoundCloud and Stitcher. Read Sapien’s investigation here, and subscribe to ProPublica’s podcasts to hear conversations like these each week.