Robert Mueller, the special counsel overseeing the federal investigation into Russian interference in the 2016 election, is looking into whether President Donald Trump tried to obstruct justice, the Washington Post reported late Wednesday.

The Washington Post reported, citing unnamed sources familiar with the matter, that the investigation into whether Trump attempted to obstruct justice began shortly after he abruptly fired James Comey as director of the FBI in May. According to the report, Mueller’s office later took up the probe.

Investigators are also searching “for any evidence of possible financial crimes among Trump associates,” according to unnamed officials cited in the report.

During his blockbuster testimony before the Senate Intelligence Committee last week, Comey said Trump was not under investigation at the time of his firing, an assertion the White House quickly seized on as a vindication of the President.

That changed shortly after Trump abruptly terminated Comey, the Washington Post reported, citing unnamed officials.

Mueller’s investigators have scheduled interviews with intelligence officials including Director of National Intelligence Dan Coats, NSA Director Mike Rogers and former deputy NSA director Richard Ledgett, the Washington Post reported, citing five unnamed sources briefed on the requests.

A spokesman for Mueller declined to comment to the Washington Post.

Mark Corallo, a spokesperson for Trump’s personal lawyer Marc Kasowitz, did not deny the report. He instead told the Washington Post: “The FBI leak of information regarding the President is outrageous, inexcusable and illegal.”