SAN FRANCISCO — Just how and why a letter sent on behalf of former Uber employee ended up in the hands of the federal judge overseeing the company's trade secret showdown with Waymo has left local legal circles abuzz—especially veterans of the San Francisco U.S. Attorney's Office.

Federal prosecutors' decision to hand over the letter—a piece of evidence that surfaced in a criminal investigation running parallel to the high profile civil showdown over autonomous vehicle technology—was a highly unusual, if not unprecedented, move.

But that's partly product of the unusual case itself. Most ex-prosecutors following the litigation said their former colleagues in the office had little choice, since the judge handling the civil case referred the criminal investigation to them. A small but vocal minority, however, said the office might have overstepped its role by butting into the civil suit and could have accidentally tripped up its own investigation in the process. A spokesman for the U.S. Attorney's Office declined to comment.

Since the letter was handed over last month, U.S. District Judge William Alsup of the Northern District of California has put off trial, reopened discovery and held three days of hearings in the civil suit that featured Uber employees and an in-house lawyer getting grillings from the judge and Waymo attorneys.

The explosive letter—which a lawyer for Uber's former manager of global intelligence Richard Jacobs sent to the company's in-house counsel in May—claimed Uber used its market analytics department to steal trade secrets from Waymo. Uber handed the letter over to multiple law enforcement agencies, including the U.S. Attorney's Office for the Northern District of California, which are looking into potential criminal and regulatory violations by the company and its employees. A team at Wilmer Cutler Pickering Hale and Dorr has also conducted an internal investigation of the letter's claims for the company.

Former federal prosecutors who discussed the office's decision to alert Alsup had varying opinions on whether prosecutors handled the matter appropriately. Most of those half-dozen former prosecutors asked not to be named for various reasons, including client concerns and their relationships with former colleagues still in the office.

The majority said the office was obliged to alert the judge about the document, since it could have a direct bearing on the civil case. Alsup, after all, referred the case to the office for a criminal investigation into possible trade secrets theft in May. They also largely sympathized with the awkward position the U.S. Attorney's Office faced by possessing a letter that hadn't surfaced in the civil litigation. It's not likely that the U.S. attorneys' manual provides clear answers about what to do in such a situation, especially in a case referred out by a judge like Alsup.

“It wasn't something done lightly,” one former prosecutor who asked to remain anonymous said of the decision. “But if it were me in the office making that decision thinking about the pros and cons, it would weigh very heavily that Judge Alsup is the type of judge who likes to have his own opportunity to assess things like this.”

UC-Hastings law professor Rory Little, a former appellate chief of the local federal prosecutors' office, agreed but said the office would likely have made the same move in any case referred out for investigation by any judge.

“If a federal judge has referred to you a matter, you're going to try to treat that judge with respect and in some respects like your client,” Little said. He added: “I'm willing to bet there was a whole lot of thinking that went on before this was handed over to the judge.”

But other office alumni claim that, by handing over the letter, the office appeared to take sides in the dispute—at least in the court of public opinion. The move, they say, gave the office's imprimatur to an internal Uber whistleblower without fully vetting his claims, potentially torpedoing its criminal case along the way.

On the witness stand, Jacobs backed away from some of the letter's most explosive allegations, including claims Uber's market analytics unit stole Waymo's trade secrets and that Uber used ex-CIA operatives to ensure company secrecy in meetings. Jacobs' testimony in the evidentiary hearing could compromise his credibility and value as a witness in any potential criminal proceeding, critics said.

If there was concern that the letter hadn't surfaced in the Waymo case, critics also said the office could have nudged Uber to disclose its existence to the judge. One former prosecutor, who asked not to be named because he's not allowed to comment publicly in his current position, said what the office did seemed “like tattling.”

“It happens all the time that a criminal investigation has more” information than would be available through civil discovery, this attorney said. “In civil discovery, it's all about gamesmanship.”

Critics also pointed out the office's decision could have a chilling effect on other witnesses who might consider coming forward in future investigations. Jacobs willingly cooperated with federal criminal investigators prior to his testimony last week, only to be forced to travel from Seattle to San Francisco on short notice to testify in the parallel civil case.

But former prosecutor Jeffrey Bornstein of Rosen Bien Galvan & Grunfeld said “there's a distinction between someone who is trying to keep a low profile and be anonymous, and someone who went on the record” as a whistleblower. Jacobs directed his 37-page letter to the company, after all.

“As a whistleblower, you assume at some point somebody is going to want to talk to you about what you're blowing the whistle on,” Bornstein said.

Alsup informed the parties he received a letter from local federal prosecutors on Nov. 22. Although portions of that letter and snippets of Jacobs' were read into the record during subsequent evidentiary hearings, the letters themselves remain under seal. They're both set to be made public on Dec. 13 at noon Pacific time, barring any appellate intervention.