Trump-Russia investigators gathering documents from estate of Republican operative, sources say

— -- U.S. Senate investigators sought and received materials from the estate of Peter W. Smith, a longtime Republican operative who reportedly acknowledged shortly before his death that he spearheaded an effort to obtain missing Hillary Clinton emails from Russian hackers, two sources familiar with the matter told ABC News.

Smith, a private-equity executive from Chicago who had been active in Republican politics, died at age 81 on May 14. Ten days earlier, he told a reporter from the Wall Street Journal that he had led a robust bid during the early months of the 2016 presidential contest to find what he thought were hacked copies of Clinton’s emails in hopes of using them against her during the campaign.

Of interest to investigators, the sources told ABC News, are documents and electronic communications that could help determine whether Smith worked in concert with anyone from the campaign of then-candidate Donald Trump. The Senate Select Committee on Intelligence has asked for those documents and the Smith estate has begun turning them over, the sources said.

William Ensing, the attorney for the Smith estate, declined to comment when reached Tuesday at his Lake Forest, Illinois office.

A spokeswoman for Sen. Richard Burr, R-N.C., the Intelligence Committee chairman, did not respond to questions, and Virginia's Sen. Mark Warner, the ranking Democrat, declined comment on the matter.

The Wall Street Journal reported in June that Smith had gathered technology experts, lawyers and a Russian-speaking investigator based in Europe to go after the emails. The news reports, citing copies of emails and other documents Smith and his team prepared, suggested that Smith received help in that effort from Lt. Gen. Michael Flynn, a senior adviser to the Trump campaign, and Flynn’s son, Michael Flynn Jr.

Attorneys from Lt. Gen. Flynn and his son both declined to answer questions from ABC News about any alleged contact between their clients and Smith.

The Senate Intelligence Committee is one of four congressional committees looking into aspects of Russia’s efforts to interfere in the 2016 election. The bipartisan effort in the Senate has focused in part on determining whether Trump advisors did anything to encourage or assist Russian agents in their efforts to influence American voters.

The companion effort by the intelligence committee in the House has been beset by partisan infighting, with House Democrats accusing GOP leadership of trying to divert attention away from Russian interference and onto other topics.

The congressional investigations are separate from the criminal probe being conducted by special counsel Robert Mueller and his team of federal prosecutors.