Schiller, who quit his White House job
in September, appeared for a closed-door interview
to the House intelligence committee on Tuesday. He was by Trump's side for many years, including the trip to Moscow, but Schiller said little to the committee about past events involving Trump, according to the sources, telling lawmakers repeatedly that he could not recall or was not aware a number of potential Russia connections with Trump associates, which Democrats continually asked about.
Trump's activities while in Moscow for that event have been the subject of rampant speculation ever since the January leak of a 35-page dossier written by former British spy Christopher Steele. The dossier also accuses the Trump campaign of colluding with Russia as part of its active measures campaign to influence the election and defeat Democratic nominee Hillary Clinton.
Several of the dossier's most salacious claims have not been independently corroborated, and Schiller denied them on Tuesday.
The hearing with Schiller provided an opportunity for lawmakers to try to learn more about the Trump campaign's contacts with Russians and Trump's links to Kremlin-friendly interests in his business career.
Schiller joined the Trump administration as director of Oval Office operations, but he left after about eight months. During the campaign, "it mattered more to me what Keith Schiller thought of me than what the campaign manager thought," a former top Trump campaign aide told CNN in May.
Being so close to Trump for so long means Schiller was around for some of the most controversial moments of Trump's political career.
Trump dispatched Schiller
in May to hand-deliver a letter to the FBI headquarters, informing then-Director James Comey of his termination. Comey was on a work trip on the other side of the country, but CNN cameras spotted Schiller entering and then leaving the FBI building.
Comey's firing is now a key part of Justice Department special counsel Robert Mueller's investigation into potential obstruction of justice. Mueller's team has recently interviewed White House witnesses who could shed light on Comey's firing. And CNN reported last week
that White House senior adviser Jared Kushner turned over documents about the firing to Mueller's investigators.
Trump has said that years earlier, Schiller joined him on a trip to Moscow for the Miss Universe pageant. The significance of the event, held in November 2013, wasn't clear at the time. But now, the contacts Trump made as part of that deal are coming back in a big way.
That deal was struck between Trump and Aras and Emin Agalarov, the father-and-son team of billionaires that own a major development firm in Russia. The Miss Universe pageant was held at one of their properties in Moscow.