Uber says its former engineer had a good reason to allegedly take Waymo's files - and it wasn't to give them to Uber

No one knows why Anthony Levandowski allegedly downloaded 14,000 proprietary files before quitting his job at Google.

But Uber, the ride-hailing company that Levandowski eventually joined and which is now being sued by Google, has a theory: It was to protect his bonus.

Levandowski had "good reason" to believe his bonus was at risk, Uber said in a legal filing on Friday.

Levandowski is a star engineer in the red-hot self-driving car industry, and he is at the center of the acrimonious lawsuit between Uber and Google.

Google, and its self-driving car spinout Waymo, sued Uber for trade theft in February. At the heart of the case is the allegation that Levandowski downloaded 14,000 files containing information on Google's self-driving car program before he left Google in late 2015. Some of those files, particularly documents relating to the lidar systems in self-driving cars, eventually made it to Uber, Waymo alleges.

Levandowski has refused to testify, relying on the Fifth Amendment protection against self-incrimination.

Uber didn't provide much insight into its theory about why Levandowski may have believed downloading the files would protect a $120 million bonus he was owed. But Uber offered a narrative in its filing on Friday that sought to prove that Uber was the furthest thing from Levandowski's mind when he downloaded the files.

The narrative

Here's the story, according to Uber:

Google had set up a bonus program for Levandowski when it acquired his self-driving car "side project" many years ago, according to the filing. The program was intended to act like an stock grant at a standalone startup - the value of Levandowski's bonus was suppose to grow in tandem with the value of the self-driving car project within Google.

But Google had shown a "grudging attitude" toward the bonus, and there was "significant tension and disagreements between Levandowski and senior managers at Google," according to the filing. As a result, Levandowski had reason to believe that Uber would undervalue the self-driving car effort, thus reducing his bonus or even possibly denying it entirely.

"That gave him every incentive to download files in December 2015, perhaps to protect his bonuses," Uber said in the filing.

Uber has denied that it used Waymo's trade secrets. And after Levandowski refused to cooperate in the case, Uber fired him.

Earlier in July, Uber dropped some of its patent claims in the case.