Carreyrou in early 2015 had just finished the story "Medicare Unmasked" for The Wall Street Journal and was looking for a new project to work on. Theranos was a healthcare tech company that had become a startup sweetheart in both the media and Silicon Valley.
"In terms of both the battle we had to wage and how multifaceted, colorful, and sheer entertaining the story has been, this has probably been the best," Carreyrou told Business Insider in a May interview. His first in a series of detailed exposs about the company was published on the front page of The Wall Street Journal in October 2015.
Carreyrou first caught wind of skepticism around Theranos back in early 2015, when Adam Clapper, a pathologist who ran an industry blog, first approached Carreyrou about Theranos.
Clapper's tip and a handful of secondhand sources helped confirm Carreyrou's gut feeling when he read a New Yorker profile on Theranos: Something was off. But Carreyrou knew that to push the story forward he'd need to talk to someone with firsthand experience at the company.
From that point, it took him about two and a half weeks to make his first contact with Beam (a pseudonym). After one phone call, Carreyrou knew he had a great story on his hands. Beam told Carreyrou everything he knew about the company. The offenses he said he witnessed included cheating on proficiency tests for the technology and providing false data to patients.
"He was the biggest hero of the story, but he was also a very reluctant hero," Carreyrou said. By speaking with Carreyrou, Beam subjected himself to speculation and relentless harassment from Theranos.
After Beam's recount, Carreyrou went back and reread past coverage on Theranos and Holmes. The lack of peer-reviewed data to back up the company's scientific claims, Holmes' vague descriptions about how Theranos' blood-testing technology worked, and the secrecy that shrouded day-to-day operations at the company stood out to Carreyrou.
It became clear to him that there was a discrepancy between what Holmes portrayed to the public and the reality, and he said that discrepancy was perpetuated through lies, including one regarding the nature of her relationship with Sunny Balwani a company executive and Holmes confidant to the board of Theranos.
Once Carreyrou started speaking with Beam, the story unraveled quickly. From there, he was able to reach many other ex-employee sources. Beam, along with a lot of the former employees, seemed traumatized by working at Theranos.
"It was like a mind-warping sort of experience," Carreyrou told Business Insider.
This article was initially published on May 21 and has been updated. Charlotte Hu contributed to an earlier version of this post.
SEE ALSO: The rise and fall of Elizabeth Holmes, who started Theranos when she was 19 and became the world's youngest female billionaire before it all came crashing down