The investigation started modestly enough — with documents anyone could have seen. Buried amid the public financial records of Universal Health Services, the largest psychiatric hospital chain in America, was a disclosure to its investors: It was under federal investigation.

BuzzFeed’s Rosalind Adams was curious. She embarked on her own investigation, to figure out, simply, why.

She built a spreadsheet of every person she could find online who was associated with the chain, from employees on LinkedIn to patients who had written reviews on Yelp. “I’m sure I called thousands of people,” she said. “This whole world opens up when you start making phone calls and asking questions.”

She talked to 18 executives who ran hospitals, cold-calling some and knocking on doors. She gained the trust of sources who slipped her security footage and insider documents.

Listen to the Podcast

After months of work, she found that multiple UHS hospitals had been accused of committing patients who didn’t need care in order to get their insurance payments, and for turning away patients who did need care, but could not pay.

Hospital CEOs told her they were instructed to use all insurance days available to them, even if a patient didn’t need to be hospitalized for that long.

Adams found that in one hospital, a 6-year-old boy who misbehaved at school was locked away for three days. In another, hospital employees were caught on video dangerously restraining a 9-year-old boy. “That’s how people die,” a nationally recognized restraint expert told BuzzFeed after seeing the footage.

UHS denied allegations that it held patients for purely financial gain, and said Adams’ work was based on “anecdotal accounts” and “personal perspectives.” The company said she drew “false conclusions” and ignored those who had positive experiences to weave a “false narrative.”

Regardless, her investigation produced results. Sen. Charles Grassley, R-Iowa, has demanded answers from UHS. One hospital lost its ability to care for foster kids and has been stripped of Medicaid funding. The FBI and the Department of Defense — which is scrutinizing billings to the military insurance plan, Tricare — launched investigations into the chain for keeping patients longer than necessary to boost profits.

Her investigation continues. Follow her on Twitter and on BuzzFeed.