A letter made public on Wednesday in Waymo's civil suit against Uber over swiped self-driving car secrets confirmed the ride-share service is the target of a US criminal investigation.

The US Attorney's Office in Northern California sent the letter to US Judge William Alsup last month to share some of what they have learned "in the course of a United States' pending criminal investigation," according to a copy of the paperwork obtained by AFP.

Alsup had referred the case to the Justice Department to look into possible criminal charges, but prosecutors remained mum after that.

Information shared by the department with Alsup sparked a courtroom furor over the possibility that Uber operated a program to hide nefarious tactics.

It also resulted in the trial being delayed a second time, with the judge setting a new start date of February 5.

The US Attorney's Office said in the missive to Alsup that they interviewed former Uber manager of global intelligence Richard Jacobs, who contended that "employees routinely used non-attributable electronic devices to store and transmit information that they wished to separate from Uber's official systems."

Attorneys representing Uber have repeatedly assured the judge no files taken from Waymo ever touched Uber servers.

Jacobs' attorney laid out his allegations in May in a letter to Uber's associate general counsel, according to the Justice document.

Alsup continues to mull whether it should have been shared during an evidence-gathering phase of the civil case.

The letter signed by Jacobs told of an effort to evade discovery requests, court orders, and government investigations "in violation of state and federal law, as well as ethical rules governing the legal profession."

Techniques used included smartphones or laptop computers that couldn't be traced back to the company, and communicating through encrypted, vanishing message service Wickr, according to the letter and a transcript of courtroom testimony obtained by AFP.

Jacobs testified that he left Uber early this year with a compensation deal valued at $4.5 million.

As part of that agreement with Uber, Jacobs remained a consultant on the payroll.

Uber executives who testified denied any wrongdoing or trail-covering.

The civil case stems from a lawsuit filed by Waymo -- previously known as the Google self-driving car unit -- which claimed former manager Anthony Levandowski took technical data with him when he left to launch a competing venture that went on to become Otto and was later acquired by Uber.

Uber is also a target of investigations and lawsuits over the cover-up of a hack that compromised personal information of 57 million users and drivers.

Uber purportedly paid data thieves $100,000 to destroy the swiped information -- and remained quiet about the breach for a year.

US justice officials are also investigating suspicions of foreign bribery and use of illegal software to spy on competitors or escape scrutiny of regulators.

Source: AFP