A top Democratic senator said Thursday that there’s “powerful” evidence that President Donald Trump’s former national security adviser, retired Lt. Gen. Michael Flynn, “broke significant criminal laws” when he accepted foreign payments.

A letter the Defence Intelligence Agency wrote to the House Oversight Committee earlier this month revealed that Flynn did not seek or gain permission to accept money from Russia’s state-owned news agency, Russia Today (RT), for a speech he gave in Moscow in 2015. The revelations were announced in a press conference Thursday.

“The evidence that Rep. Cummings just outlined is powerful, mounting, incontrovertible evidence that there has been a violation of criminal law,” Sen. Richard Blumenthal said at the press conference, referring to Rep. Elijah Cummings, the ranking member on the House Oversight Committee.

“This evidence is powerful in showing that Gen. Flynn broke significant criminal laws,” Blumenthal said. “The DIA letter, the DOD letter, the inspector general letter, all testify to a flagrant violation of federal criminal statutes that must be investigated and prosecuted.”

Reps. Jason Chaffetz and Cummings, the top Republican and Democrat on the House Oversight Committee, said in a joint press conference on Tuesday that Flynn appeared to have broken the law.

The DIA letter saying Flynn did not seek permission from the agency before accepting the RT payment appears to contradict a statement Flynn’s lawyer released on Tuesday.

“As has previously been reported, General Flynn briefed the Defence Intelligence Agency, a component agency of the Department of Defence, extensively regarding the RT speaking event trip both before and after the trip,” Robert Kelner, Flynn’s lawyer, said in the statement.

But Flynn, who headed the DIA between 2012 and 2014, did not brief the agency on the thousands of dollars he received from RT to speak at its 10th anniversary gala, according to the DIA. In failing to disclose the payment, Flynn may have violated the Emoluments Clause of the US Constitution, which prohibits retired military personnel from receiving payments from foreign sources without advance permission.

Blumenthal called for a special prosecutor to investigate Flynn and others in the Trump administration who might have connections to foreign governments.

“For all the reasons that Rep. Cummings outlined so powerfully about the White House seeking, in effect, to cover up for Gen. Flynn, we can’t count on the attorney general or his deputy, who report to the president of the United States and the White House, to do that job,” Blumenthal said. “There needs to be a special prosecutor.”

He also called for a special prosecutor to investigate “the conflicts of interest on the part of President Trump and others in the White House.”

Flynn was forced to step down from his position in February after only 24 days amid revelations that he misled Vice President Mike Pence about his conversations with Russia’s ambassador to the US, Sergey Kislyak.

Flynn last month offered to testify before the congressional intelligence committees in exchange for immunity from prosecution — a signal to some legal experts that he thought he may have committed a crime. Neither of the committees have taken him up on the offer.

Natasha Bertrand contributed to this report.

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