WASHINGTON — Ever since American intelligence agencies accused Russia of trying to influence the American election, there have been questions about the proof they had to support the accusation.

But the news from Moscow may explain how the agencies could be so certain that it was the Russians who hacked the email of Hillary Clinton’s campaign and the Democratic National Committee. Two Russian intelligence officers who worked on cyberoperations and a Russian computer security expert have been arrested and charged with treason for providing information to the United States, according to multiple Russian news reports.

As in most espionage cases, the details made public so far are incomplete, and some rumors in Moscow suggest that those arrested may be scapegoats in an internal power struggle over the hacking. Russian media reports link the charges to the disclosure of the Russian role in attacking state election boards, including the scanning of voter rolls in Arizona and Illinois, and do not mention the parallel attacks on the D.N.C. and the email of John Podesta, Mrs. Clinton’s campaign chairman.

But one current and one former United States official, speaking about the classified recruitments on condition of anonymity, confirmed that human sources in Russia did play a crucial role in proving who was responsible for the hacking.