Did Robert Mueller just drop a hint that the probe on Russian collusion has some unhappy surprises for Donald Trump? In documents filed with the court late last night, Mueller specified that a person of interest in the investigation that had contact with Rick Gates and Paul Manafort had connections to Russian intelligence. The specific change seems to be an assertion that those connections and contacts took place in 2016 and not just in their past business with Russian-backed Ukrainian politicians:

The FBI has found that a business associate of former Trump campaign chairman Paul Manafort had ongoing ties to Russian intelligence, including during the 2016 campaign when Manafort and his deputy, Rick Gates, were in touch with the associate, according to new court filings.

The documents, filed late Tuesday by prosecutors for special counsel Robert S. Mueller III, also allege that Gates had said he knew the associate was a former officer with the Russian military intelligence service.

This filing apparently does not come in the case against Gates or Manafort, intriguingly. It’s an update on the case against London attorney Alex van der Zwaan, who also pled guilty to charges and is awaiting sentencing:

Fourth, the lies and withholding of documents were material to the Special Counsel’s Office’s investigation. That Gates and Person A were directly communicating in September and October 2016 was pertinent to the investigation. Federal Bureau of Investigation Special Agents assisting the Special Counsel’s Office assess that Person A has ties to Russian intelligence service and had such ties in 2016. During his first interview with the Special Counsel’s Office, van der Zwaan admitted that he knew of that connection, stating that Gates told him Person A was a former Russian Intelligence Officer with GRU.

For those keeping score, van der Zwaan is the son-in-law of a Russian oligarch, German Khan, one of the owners of Alfa Bank, and had extensive dealings with Manafort on his earlier work for the Yanukovych regime in Ukraine. He’d be in position to know who the players were. According to the Post’s account, van der Zwaan attempted to hide those connections, both by misleading investigators and withholding documents, until they formally interrogated him about the matter.

Why would he do that, when the connection to Person A had been known for months?He’s identified as Person A in the new filing, but as Aaron Blake notes, it’s widely assumed to be a Ukrainian aide to Gates and Manafort named Konstantin Kilimnik. His association with Gates and Manafort had been previously known, but not that those contacts continued into the presidential campaign. That makes Kilimnik veeeeeery interesting for investigators:

What’s particularly significant in the Mueller filing, though, are six words: “and had such ties in 2016.” Prosecutors have said previously that a longtime Manafort and Gates associate had ties to Russian intelligence, but they have never said those ties remained during the 2016 campaign. In December, they said this associate was “a longtime Russian colleague . . . who is currently based in Russia and assessed to have ties to a Russian intelligence service.” Why those six words were added in this filing when they didn’t appear in a previous filing is the $64,000 question.

The other new piece here is that they say Gates described Person A (again, apparently Kilimnik) as “a former Russian Intelligence Officer with GRU.” (GRU is Russia’s military intelligence organization.) So according to van der Zwaan, Gates talked openly about Person A’s ties to Russian intelligence. Kilimnik told The Post in June that he has “no relation to the Russian or any other intelligence service.” Mueller is now apparently directly disputing that using Gates’s own words.

However, Manafort had already acknowledged contacts with Kilimnik in 2016:

Manafort has acknowledged staying in frequent contact with Kilimnik during the time he worked for Trump’s campaign, including meeting with him in person in May 2016 and again in August 2016, about two weeks before Manafort resigned as Trump’s campaign chairman.

A Manafort spokesman expressed confidence in June that investigators would ultimately conclude that Manafort’s interactions with Kilimnik were “perfectly permissible and not in furtherance of some conspiracy.”

Politico’s Kyle Cheney remains cautious on whether this means much — yet:

The filing shed little light on whether Americans aided Russia’s interference in the 2016 election, but it shows that prosecutors believe a top Trump official remained in contact with a Russian intelligence-linked operative well into the campaign. …

Gates remained in touch with “Person A” late in the campaign, Mueller said, communicating with the associate and van der Zwaan in a “series of calls” in September and October of 2016.

It might not mean much — but if it didn’t, why would van der Zwaan (and possibly Gates) try to keep it from investigators and risk an obstruction of justice charge? We will not likely get an answer to that question any time soon, but the contacts between Kilimnik and Gates in September and October of 2016 while Gates was still working on the campaign are undeniably curious, at the very least.

Update: And of course, the biggest issue here is that Gates himself admitted to van der Zwaan that he knew of Kilimnik’s relationships with Russian intel at the time. Whether Gates has an explanation for keeping those contacts while on the Trump campaign remains to be seen.