In 2017, Waymo sued Uber, accusing it of stealing self-driving technology. The two companies settled the case four days into the trial, with Uber agreeing to give 0.34 percent of its stock to Waymo’s parent company, Alphabet. The federal judge presiding over the case, however, referred the matter to the United States attorney’s office in San Francisco to investigate whether Mr. Levandowski had violated the Economic Espionage Act.

“All of us have the right to change jobs,” the United States attorney, David L. Anderson, said. “None of us has the right to fill our pockets on the way out the door. Theft is not innovation.”

Miles Ehrlich, one of Mr. Levandowski’s lawyers, said that “the evidence in this case is going to show conclusively that Anthony did not steal anything.”

So what exactly is a trade secret under the Economic Espionage Act?

The statute defines a trade secret as “all forms and types of financial, business, scientific, technical, economic or engineering information, including patterns, plans, compilations, program devices, formulas, designs, prototypes, methods, techniques, processes, procedures, programs or codes, whether tangible or intangible, and whether or how stored, compiled or memorialized physically, electronically, graphically, photographically or in writing.” That seems to cover just about all forms of intellectual property.

But for information to qualify as a trade secret, its owner must take “reasonable measures to keep such information secret” and derive “independent economic value” from its not being generally known. Prosecutors must also show that a trade secret was acquired by “improper means.” That means proof it was taken by “theft, bribery, misrepresentation, breach or inducement of a breach of a duty to maintain secrecy, or espionage through electronic or other means.” But the law does not cover reverse engineering or any other “lawful means of acquisition.”