Enlarge (credit: Bloomberg / Getty Images News) A newly-released letter has formally acknowledged what was only briefly stated last month in a San Francisco courtroom: federal prosecutors have an open criminal investigation into Uber. Late last month, as part of the proceedings in the high-profile and ongoing Waymo v. Uber trade secrets lawsuit, US District Judge William Alsup said that on November 22 he had received a letter from San Francisco-based federal prosecutors. It is very unusual for a judge in a civil case to be apprised of a pending criminal investigation involving one of the litigants. In a separate November 28 letter sent to Judge Alsup, Acting US Attorney Alex Tse asked that the first letter not be made public.