In this photo taken on Sunday, April 21, 2013, Maria Butina, leader of a pro-gun organization in Russia, speaks to a crowd during a rally in support of legalizing the possession of handguns in Moscow, Russia.

The Justice Department on Monday revealed it had arrested prominent Russian gun rights activist Maria Butina over the weekend, accusing her of setting up "back channel" lines of communication with the Kremlin in an operation that spanned from the months before Trump announced his candidacy in 2015 through February 2017, the month after his inauguration.

In the unsealed indictment, the department accused Butina of conspiring to infiltrate U.S. political groups and advance the agenda of the Russian government through her network of high-profile American contacts in politics and media.

The indictment includes the most explicit and detailed accusation to date against a Russian, working with the help of an American citizen, to influence the 2016 presidential election. It also provides new details about the Russian government's attempts to curry favor among prominent Americans.

Notably, the charges are not being made by special counsel Robert Mueller, who is probing Russia's attempts to meddle in the 2016 election. The investigation was carried out by the FBI's field office in Washington, and Butina is being prosecuted by the U.S. Attorney’s Office for the District of Columbia and the Justice Department's national security division.

Nonetheless, the timing of the charge is critical. Butina was arrested just two days after Mueller announced charges against 12 Russians for hacking into computers belonging to the Democratic National Committee and Hillary Clinton, and just a day before Trump appeared with Putin in Finland and publicly questioned his intelligence community's assessment that Russia interfered in the 2016 election to bolster Trump's odds.

The president is not mentioned directly in the indictment. But the two were captured on camera in an exchange between Butina and then-candidate Trump at a Las Vegas campaign event in 2015. At the "FreedomFest" gathering, Butina asked Trump what he thought about sanctions on Russia. Trump responded that he had a good relationship with Putin and "I don’t think you’d need the sanctions."

In an affidavit filed with the indictment, FBI special agent Kevin Helson accuses Butina of working with a "U.S. Person 1," who has been identified as Paul Erickson, a longtime GOP consultant who advised Mitt Romney and Pat Buchanan.

Erickson and Butina appear jointly on the filings of a South Dakota business called "Bridges LLC," and are personal friends. The Daily Beast reported last February that Erickson dressed in costume as Rasputin at Butina's birthday party held shortly after the 2016 presidential election.

Butina's Russian supervisor in the indictment, referred to only as a Russian official, has been widely identified as Alexander Torshin, a former Russian senator and longtime supporter of the NRA. Torshin is the deputy head of Russia's central bank, and has been sanctioned by the U.S. Treasury Department and linked to organized crime. The FBI has investigated Torshin for using the NRA as a conduit for funds that would help Trump win the presidency, McClatchy reported earlier this year.

Butina's attorney Robert Driscoll said the charges were "overblown" in a written statement, pointing to Butina's 4.0 GPA at American University and noting that Butina had cooperated with the Senate Intelligence Committee and offered to sit for an interview with Mueller, who, he said, has not expressed interest. Driscoll said Butina had offered repeatedly to cooperate with the Department of Justice as well, but it had chosen to arrest her without notice.

The NRA did not respond to a request for comment, and Erickson could not immediately be reached by CNBC. In a statement posted to Twitter, the Russian embassy in Washington wrote, "We are in contact with the US authorities and demand from them consular access to the Russian citizen in order to protect her legitimate rights"