When Rep. Adam Schiff, the Democratic chairman of the House intelligence committee, asked, "Your investigation is not a witch hunt, is it?" "It is not a witch hunt," Mueller flatly replied.
In high-stakes testimony, Mueller said that the Russians engaged in sweeping interference in the 2016 US Presidential election.
The televised Capitol Hill appearances, Mueller's first since wrapping his two-year Russia probe last spring, are unfolding at a moment of deep divisions in Congress and the country.
The Judiciary Committee aides said that they want lawmakers to take multiple pieces of information in Mueller's report and connect the dots for viewers.
Mueller had been previously scheduled to testify July 17 before two house committees about the findings of his Russia investigation.
Mueller will testify before both committees on July 17 about his investigation against alleged Russian meddling in the 2016 US presidential elections.
Trump, who has assailed the Russia investigation as a treasonous "witch hunt" and a "hoax," declared the case over.
Over 22 months, prosecutors issued charges against 34 individuals, including six Trump associates, and three companies.
Mueller reiterated that his report into Russian interference in the 2016 election and potential obstruction of justice did not exonerate the president.
Adam Schiff said he requested those documents in order to gauge whether the department was acting in good faith.
The two leaders also discussed the political and humanitarian crisis in Venezuela, nuclear agreements, North Korea and trade, Sanders added.
A rift between the special counsel's office and Barr, Mueller's boss and longtime friend, appeared to emerge in the days following the release of the attorney general's memo.
The Russian government suggested that US taxpayers should question why their money was spent on the lengthy probe with such a result.
Donald Trump's initial reaction to Mueller's appointment was 'this is the end of my Presidency': Report
Trump once feared Mueller could destroy his presidency, but the special counsel may instead define it.
Barr said Mueller investigated a number of links or contacts between Trump Campaign officials and individuals connected with the Russian government.