What if an act meant to protect a colleague actually put patients at risk and “violated all [the] pledges of professionalism that came with the Doctor of Medicine degree"?

A doctor in South Dakota is now sharing his experience with doing exactly that with ProPublica: he lied to protect a partner in his surgical practice from a malpractice suit. Even though he knew the doctor in question sometimes performed sub-standard care practices that resulted in harm to patients, Lars Aanning didn’t reveal his concerns under oath.

Aanning kept his untruth secret for almost 20 years—until he retired. Now he’s talking about what he did and why in an effort to advocate for patients who might not be getting the full truth from their doctors when it comes to care mistakes.

He said he didn’t feel like it was a conscious effort to obscure the truth at first, only an effort to protect a business associate. He wants to uncover this culture of implicit protectionism among physician colleagues so patients and attorneys can get a better idea of what might be happening behind the scenes when it comes to malpractice cases.

Check out ProPublica’s conversation with Aanning at NPR to see how he feels now that the truth is out in the open and what he still can’t bear to face about the situation.