Federal prosecutors have ended an investigation into Democratic lobbyist Tony Podesta and former Rep. Vin Weber, R-Minn., in a case connected to lobbying for Ukraine and Paul Manafort without filing criminal charges, multiple sources familiar with the matter tell NBC News.

The investigation by the Southern District of New York, which focused on whether several prominent Washington lobbyists violated foreign lobbying rules, grew out of special counsel Robert Mueller's inquiry into the finances of Manafort, a former Trump campaign chairman who is now serving a 7.5 year sentence in federal prison.

Manafort had organized a public relations campaign for a nonprofit called the European Centre for a Modern Ukraine, which promoted Ukraine's image in the West from 2012 to 2014. Podesta's Democratic-leaning lobbying firm, the Podesta Group, was one of many firms that worked on the campaign, including Weber's firm, Mercury Public Affairs.

NBC News was the first to report in 2017 that Podesta and his firm had been ensnared in Mueller’s probe because of their work on the campaign.

Podesta is the chairman of the Podesta Group and the brother of John Podesta, who was Hillary Clinton's presidential campaign chairman. John Podesta has not been affiliated with the Podesta Group since the 1990s and was not a subject of the investigation.

Both firms were being investigated for possibly failing to file Foreign Agents Registration Act reports for their work with the ECMU and on behalf of Ukraine, NBC News has previously reported.

According to an October 2017 indictment, the two lobbying firms were paid $2 million from offshore accounts controlled by Manafort for their work on the campaign.

In a statement to NBC News, Vin Weber’s attorney said they had been notified the investigation was over.

“As we have previously stated, at all times Mr. Weber acted in good faith and in keeping with the legal advice his company received from its outside counsel,” Weber’s attorney Robert Trout said.

“We are obviously pleased by this development,” Trout added.

Podesta did not immediately respond to a request for comment. A spokesperson for the Southern District of New York declined to comment.

The dropping of the investigation comes on the heels of the not guilty verdict in the trial of former Obama White House counsel Greg Craig, another case that Mueller's office had passed to federal prosecutors in the Southern District of New York.

In that case, the New York attorneys decided not to prosecute, sources said, and the case was ultimately brought by federal prosecutors in Washington, only to result in an acquittal for Craig.

Several people briefed on the Podesta and Weber probe told NBC News they thought that the investigation into the two lobbyists had a better chance of succeeding than the probe into Craig, but in the end the legal hurdles would’ve been too high.