There's a good reason why Anthony Levandowski doesn't want to testify, Uber says. Otto 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 Google 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.

Waymo's response

A Waymo spokesman dubbed Uber's bonus narrative "fictitious."

In recent court filings, Waymo has tried to make the case that Levandowski had no reason to worry about his bonus.

In a court document Waymo filed on Monday, the company said that Levandowski was paid his bonus in December 2015 on time and was paid the last of his bonuses in April 2016 — also on time. In a separate document filed on Friday in response to Uber's assertions, Waymo said the company's explanation for Levandowski's actions "doesn't follow logically. And the idea that Levandowski was owed money that was overdue was "simply wrong," Waymo said.

"The notion that Levandowski would subject himself to criminal liability by stealing Waymo’s proprietary information and holding it 'ransom' for his performance bonus strains credibility," Waymo said in the filing.

Why it matters

The dueling court filings are part of a battle over whether Levandowski's invocation of the Fifth can be mentioned in a possibly trial and how it could be characterized. Waymo is urging the court to allow it to portray Levandowski's refusal to testify in a negative light, saying that it helps show Uber's culpability. Waymo argues that by taking the Fifth, Levandowski is protecting not only himself but Uber and by making it more difficult for Waymo to show that Uber had knowledge of the allegedly stolen files.

Uber is fighting that effort and disputing that notion. It's trying to show that Levandowski has other reasons not to testify that have nothing to do with it.

The battle over Levandowski's refusal to testify is only the latest turn in the case. Earlier in July, Waymo dropped some of its patent claims in the lawsuit.