Levandowski is at the heart of an ongoing legal battle between Uber and Google's self-driving auto division Waymo.
The case prompted Levandowski in April to temporarily step aside as Uber's top self-driving auto executive and avoid working on anything related to lidar, an array of sensors that enables autonomous vehicles to navigate the roads.
Levandowski already had stepped down from his position as head of Uber's self-driving auto efforts last month and was replaced by Eric Meyhofer. Levandowski then helmed Uber's Advanced Technologies Group, the company's internal autonomous vehicle division, until April, when he stepped aside amid PR fallout from the lawsuit.
Waymo had accused Uber of protecting Levandowski, but at Alsup's behest, the ride-hailing giant earlier this month ordered Levandowski to either return any files he took while working at Google, formally deny taking the files, or risk termination.
A source familiar with the matter said Levandowski had not yet vested his Uber shares.
San Francisco-based Uber appears to be blaming the stolen documents exclusively on Levandowski in an effort to defend itself against Waymo's lawsuit.
Asked last month why Uber did not threaten to fire Levandowski to pressure him into turning over the documents, Uber attorney Arturo Gonzalez told Reuters, "We can fire him but we still don't get the documents".
Uber said his refusal to hand over those documents - a key piece of evidence in the lawsuit between Uber and Google's parent company - violated the terms of his employment. Business Insider reported Tuesday that in the weeks before his firing, he invoked the Fifth Amendment and hired outside counsel. But US District Court Judge William Alsup criticised the company, telling lawyers: "You keep on your payroll someone who took 14,000 documents and is liable to use them".
The letter also revealed that Uber required Levandowski to have "returned or destroyed all property and confidential information belonging to any prior employer" as a condition of his employment.
"What prevented him from bringing a laptop to work every day and consulting the files?"
Uber in April removed Mr. Levandowski from its driverless-car program. Earlier this year, Uber was caught using its technology to avoid government regulators.
The company will release the findings of a three-month-long investigation into alleged sexual harassment in the workplace later this week.