Federal prosecutors investigating Rudy Giuliani’s links to two Soviet-born businessmen arrested last week on campaign finance charges have reviewed the former New York City mayor’s bank records, the Wall Street Journal reported Monday night.

Investigators are looking at Giuliani’s finances, meetings and work for a city mayor in Ukraine as part of the probe, unnamed people familiar with the matter told the Journal. They have been questioning witnesses for the probe since August, the Journal reported.

The criminal probe into Giuliani is being led by U.S. attorney’s office for the Southern District of New York.

Giuliani, who has served as President Trump’s personal lawyer, has come under intense scrutiny over the past few weeks as details emerge about a pressure campaign on Ukraine carried out by Giuliani and members of the Trump administration.