Roger Stone, the longtime ally of President Trump's known for his brash and braggadocio style, answered questions behind closed doors from lawmakers and staff for the House Intelligence Committee for more than three hours Tuesday, as part of the panel's ongoing investigation into Russia's interference in the 2016 election.

In his opening statement, which was reported in the press prior to his appearance, and in speaking to reporters after his interview, Stone took issue with an investigation he called an "entirely political exercise."

"I expressed my view that I am aware of no evidence whatsoever of collusion by the Russian state or anyone in the Trump campaign," Stone told reporters.

Stone is of great interest to investigators because of things he has said.

Last year, it appeared that he may have known about stolen Clinton campaign emails before they were leaked, saying Clinton campaign chairman John Podesta would "have his time in the barrel," two days before Podesta's emails were released.

And Stone has also been open about communications with a Web persona, Guccifer 2.0, linked to Russian cyberattackers who the intelligence community believes were behind last year's hack of the Democratic National Committee. Stone attached his Twitter messages with Guccifer 2.0 to his opening statement to the committee.

Stone said Tuesday's line of questioning focused mostly on these interactions.

"While some may label me a dirty trickster, the members of this Committee could not point to any tactic that is outside the accepted norms of what political strategists and consultants do today," Stone said in his opening statement. "I do not engage in any illegal activities on behalf of my clients or the causes in which I support.

"There is one 'trick' that is not in my bag and that is treason."

After his interview, Stone said he answered all of the committee's questions but refused to identify a journalist who acted as an intermediary between him and WikiLeaks publisher Julian Assange.

The committee's ranking Democrat, Rep. Adam Schiff of California, said Stone could be subpoenaed to return to answer questions related to that interaction.

"Hopefully, he will cooperate in the future," Schiff said, according to Reuters. "If not, it will be necessary to subpoena him to bring him back to answer those important questions."

Stone said he has not yet been contacted by special counsel Robert Mueller, who is leading the Justice Department's Russia investigation. And he added that he had spoken to President Trump "recently" but not about Tuesday's appearance or "this investigation."

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