Former U.S. Secretary of Defense testifies in court to being duped by Elizabeth Holmes of Theranos

Former U.S. Secretary of Defense James Mattis testified Wednesday in the trial of fallen tech star Elizabeth Holmes, saying the entrepreneur misled him into believing she was on the verge of rolling out a blood-testing breakthrough that he hoped would help save lives of troops in battle.

Mattis' appearance came during the sixth day of a high-profile trial in San Jose, California. The U.S. government alleges that Holmes duped sophisticated investors, patients, customers and even her own company's board into believing that her startup, Theranos, had developed a technology that could scan for an array of potential health problems with just a few drops of blood. Existing tests generally each require a vial of blood.

During more than three hours of maskless testimony delivered behind plexiglass, Mattis recalled how impressed he was with Holmes when he first met her in 2011 while still serving as a four-star general in the Marine Corps, where he oversaw U.S. wars in Iraq and Afghanistan.