Rudy Giuliani's relationship with arrested men is subject of criminal investigation: Sources Two sources familiar with the matter confirmed.

The business relationship between President Donald Trump's private lawyer Rudy Giuliani and the men charged Thursday in a campaign finance scheme is a subject of the ongoing criminal investigation being conducted by federal authorities in New York, according to two sources familiar with the matter.

The investigation became public after the FBI had to quickly move to arrest Lev Parnas and Igor Fruman before they boarded a flight out of the country from Washington Dulles Airport with one-way tickets. They have been named as witnesses in the ongoing impeachment inquiry into President Trump.

The investigation is being conducted by the FBI's New York field office and prosecutors in the Southern District of New York, the same U.S. Attorney's office Giuliani ran before he became mayor of New York.

Giuliani has declined to comment on the case.

Parnas and Fruman, two Soviet-born, Florida-based businessmen, assisted Giuliani in his effort to dig up dirt on Joe Biden and his family. The association among the three men goes back several years. Giuliani has represented Parnas and Fruman in the past.

The two men were charged Thursday with four counts, including conspiracy to commit campaign finance fraud, false statements to the Federal Election Commission, and falsification of records.

Two associates of Parnas and Fruman, David Correira and Andrey Kukushkin, were indicted along with Parnas and Fruman on Thursday. William Sweeney, FBI assistant director in charge of the New York Field office, said at a Thursday news conference that Kukushkin was taken into custody in San Francisco, while Correia had yet to be arrested.

In his first reaction to the indictments on Thursday, President Trump said he doesn't know the associates of Rudy Giuliani -- even though he may be in a photo with one of them.

"I don't know those gentleman. That is possible I have a picture with them because I have a picture with everybody -- I have a picture with everybody here. But somebody said there may be a picture with -- at a fundraiser or somewhere so, but I have pictures with everybody. I don't know if there's anybody I don't have pictures with. I don't know them," Trump said.

"You have to ask Rudy. I just don't know," Trump told reporters as he departed the White House on his way to a political rally in Minnesota on Thursday.