Eric Swildens knows how damaging intellectual property trials can be. In 2002, Speedera Networks, the content delivery network he cofounded, was sued for patent infringement and trade secrets violation by Akamai. “It was trial by fire,” says the 50-year-old engineer. “I learned a bunch of stuff I didn’t necessarily want to learn.”

Mark Harris is a freelance journalist reporting on technology from Seattle. Sign up to get Backchannel's weekly newsletter, and follow us on Facebook, Twitter, and Instagram.

After a three-year battle in which he spent up to $1000 an hour on lawyers, Swildens ended up selling Speedera at a discount to Akamai for $130 million.

The experience left Swildens with a working knowledge of intellectual property battles in the tech world, and a lingering soft spot for others facing hefty patent claims. So when he heard in February that the world’s second-most valuable company, Alphabet, was launching a legal broadside at Uber’s self-driving car technology, he put himself in then-CEO Travis Kalanick’s shoes: “I saw a larger competitor attacking a smaller competitor…and became curious about the patents involved.”

In its most dramatic allegations, Waymo is accusing engineer Anthony Levandowski of taking over 14,000 technical confidential files to Uber. But the company also claimed that Uber’s laser-ranging lidar devices infringed four of Waymo’s patents.

“Waymo developed its patented inventions…at great expense, and through years of painstaking research, experimentation, and trial and error,” the complaint read. “If [Uber is] not enjoined from their infringement and misappropriation, they will cause severe and irreparable harm to Waymo.”

But Swildens had a suspicion. He dug into the history of Waymo’s lidars, and came to the conclusion that Waymo’s key patent should never have been granted at all. He asked the US Patent and Trademark Office (USPTO) to look into its validity, and in early September, the USPTO granted that request. Days later, Waymo abruptly dismissed its patent claim without explanation. The USPTO examiners may still invalidate that patent, and if that happens, Waymo could find itself embroiled in another multi-billion-dollar self-driving car lawsuit—this time as a defendant.

Prosecuting a patent in a lawsuit is a risky business. Patents undergo intense scrutiny during a trial, where many are shown to be poorly written, inapplicable, or even to have been granted in error. But Waymo thought it had a slam dunk for a big patent win. Public records seemed to show Uber using its technology, and an email from a supplier contained an Uber circuit board almost identical to its own lidars.

As the legal discovery process unfolded, however, it turned out that three of its four patent claims applied only to an outdated lidar, codenamed Spider, that Uber was no longer developing. When in early July the ride-sharing company promised to abandon the Spider design and never revive it, Waymo dropped those claims.

But one claim remained, related to a patent nicknamed 936. The 936 patent describes a laser diode firing system that generates the pulses of light a lidar uses to build a 3D picture of the world around it. Waymo believed that just such a circuit was present in Uber’s current generation of lidar, codenamed Fuji. But when Swildens looked it over, he was surprised by how basic the firing system looked.

“You’re talking about a capacitor, a laser diode, a transistor, an inductor, and some other diodes,” Swildens tells me from his home in Los Altos Hills, near Mountain View. “It’s a very simple circuit. When I initially saw it, I couldn’t imagine the circuit didn’t exist prior to this patent.”

In mid-July, he started looking for places where that circuit might have been described previously. If an invention claimed in a patent can be shown to have existed or been described previously, it is called “prior art” and generally invalidates the patent. Prior art can be other patents, products offered for sale, or even books. “I was ready to give up at any time,” he says. “If it seemed to pan out as some super invention, I’d have quit working on it.”