For decades, Swiss chemical giant Syngenta has manufactured and marketed a widely used weed-killing chemical called paraquat, and for much of that time the company has been dealing with external concerns that long-term exposure to the chemical may be a cause of the dreaded, incurable brain ailment known as Parkinson’s disease.

The New Lede — in a collaboration with The Guardian — published a story that examines what Syngenta knew about the evolving science linking the pesticide to the disease.

The story is based on hundreds of pages of internal corporate records that reveal conversations between scientists and executives dating back to the late 1950s.

The files demonstrate that while Syngenta has repeatedly told customers and regulators that scientific research does not prove a connection between its weedkiller and the disease, the public narrative put forward by the company and the corporate entities that preceded it has at times contradicted the company’s own research and knowledge.