... brick by brick, Robert Mueller continues to build the case for collusion against Gates, Manafort and Donald Trump.

Mueller: Gates, Manafort Trump Russia Collusion

(CNN) — Special counsel Robert Mueller's team last year made clear it wanted former Trump campaign deputy Rick Gates' help, not so much against his former business partner Paul Manafort, but with its central mission: investigating the Trump campaign's contact with the Russians. New information disclosed in court filings and to CNN this week begin to show how they're getting it.

In a court filing earlier this week, the public saw the first signs of how the Mueller team plans to use information from Gates to tie Manafort, the former Trump campaign chairman, directly to a Russian intelligence agency. Mueller's team alleges that Gates was in contact with a close colleague of Manafort's who worked for a Russian intelligence agency -- and that Gates knew of the spy service ties in September and October 2016, while he worked on the Trump campaign. Gates would have to talk about the communication with the man if prosecutors wanted, according to his plea deal.

The alleged Russian intelligence agent, referred to as "Person A" in the court filing, appears to be Konstantin Kilimnik, a former employee who worked with Manafort's firm and lived in Kiev and Moscow, according to sources familiar with the investigation. In December, the Mueller prosecutors made a similar unnamed reference to Kilimnik, saying he is "assessed to have ties to a Russian intelligence service." That was related to a Kiev newspaper op-ed that Kilimnik helped edit in consultation with Manafort late last year, which prosecutors said could violate a court-imposed gag order on Manafort.

A chief criticism from President Donald Trump and his defenders has been that the charges brought so far by the special counsel don't relate directly to Mueller's central mission investigating possible illegal coordination between the Trump campaign and the Russian government, which the President and others often shorthand using the term collusion. The accusation related to Kilimnik and ties to Russian intelligence, made in Mueller's Tuesday filing, begins to answer that criticism, but so far without actually making the charge in Manafort's case.