A court document filed by Special Counsel Robert Mueller's prosecutors Tuesday night has an interesting footnote about Rick Gates, President Trump's former deputy campaign manager and cooperating witness in Mueller's investigation. Gates was "directly communicating in September and October 2016" with an unidentified person who "has ties to a Russian intelligence service and had such ties in 2016," and Gates knew about this person's ties to Russian intelligence, the filing says, calling the 2016 conversations "pertinent to the investigation."

NBC News: Here's the filing. Person A is identified in previous pages as an associate of Paul Manafort: pic.twitter.com/zWkY8vTZRR — Tom Winter (@Tom_Winter) March 28, 2018

The court filing was mostly about the upcoming sentencing hearing of Dutch lawyer Alex van der Zwaan, who admitted to lying to Mueller's investigators and is seeking to avoid jail time. Van der Zwaan is seeking leniency at his April 3 sentencing because his wife, Eva Khan, is giving birth to their first child in August. Khan's father is Russian billionaire German Khan, who cofounded the Alfa banking group; computer scientists noticed mysterious communications between Alfa Bank servers and a Trump Organization server in 2016, and an investigation into the communications was apparently inconclusive.

Lawyers for Van der Zwaan, who does not have a cooperation deal with Mueller's team, said in their filing Tuesday night that Gates and the unidentified Eastern European ("Person A") warned van der Zwaan in 2016 about a possible criminal case in Ukraine against him and his firm, Skadden, Arps, Slate, Meagher & Flom, for work he had done with Gates. Van der Zwaan secretly recorded the "unusual and unnerving" conversations, his lawyers said, and he initially lied about the communications because he didn't want to be fired. He was fired anyway. Mueller's office describe the calls as "memorable." Peter Weber