Jim Mattis testifies that Elizabeth Holmes misled him about Theranos

• Mattis joined the Theranos board in 2013 and invested $85,000 of his own money into the company, shortly after retiring from the military. He said that he believed that the technology could help save the lives of troops on the battlefield.

What they're saying: "There just came a point where I didn’t know what to believe about Theranos anymore," Mattis said, per the Journal.

• Mattis said that after Holmes showed him the technology, he "did not want to miss an opportunity."

Catch up quick: A series of stories from the Journal revealed that Theranos' technology did not work as advertised, which led several investors to sue the company.

• Theranos is considered "the biggest fraud to have ever come out of Silicon Valley," Axios' Kia Kokalitcheva writes.

What to watch: Other Theranos board members include former Cabinet members and CEOs, AP notes. Some are expected to testify during the trial, which is scheduled to continue until December.