An associate of Rudy Giuliani who was involved in a campaign to pressure Ukraine into aiding President Donald Trump’s political prospects has broken ranks, opening a dialogue with congressional impeachment investigators and accusing the president of falsely denying their relationship.

The associate, Lev Parnas, had previously resisted speaking with investigators for the Democrat-led impeachment proceedings, which are examining the president’s pressure attempts in Ukraine. A former lawyer for Trump was then representing Parnas.

But since then, Parnas has hired new lawyers who contacted the congressional investigators last week to notify them to “direct any future correspondence or communication to us,” according to a copy of the letter.

The lawyers also signaled Monday that Parnas is prepared to comply with a congressional subpoena for his documents and testimony.

Parnas, a Ukrainian-born American citizen who was central to Giuliani’s efforts to dig up dirt on Trump’s rivals, could offer Congress a vein of information about the efforts in Ukraine.

“We are willing to comply with the subpoena to the extent that it does not violate any appropriate privilege that Mr. Parnas may properly invoke,” said Joseph A. Bondy, who along with Edward B. MacMahon Jr. now represents Parnas.

Bondy said that given the federal criminal charges, his client may invoke his right under the Fifth Amendment not to incriminate himself.

The turnabout occurred after their client was arrested last month on federal campaign finance charges and Trump denied knowing him.

“Mr. Parnas was very upset by President Trump’s plainly false statement that he did not know him,” said Bondy, whose client has maintained that he has had extensive dealings with the president.

After federal prosecutors in Manhattan announced campaign finance charges against Parnas and three other men, Trump told reporters that he did not know Parnas or Igor Fruman, another Giuliani associate who also worked to help Trump in Ukraine and was among those charged with campaign finance violations.

The two men had contributed extensively to political committees supporting Trump and appeared with the president in pictures posted on social media.

“I don’t know them. I don’t know about them. I don’t know what they do. … Maybe they were clients of Rudy. You’d have to ask Rudy,” he said. Of the numerous photographs of them together, Trump said, “I have a picture with everybody.”

Parnas hired Giuliani in 2018 to help with a venture called Fraud Guarantee. But as of early this year, their relationship had shifted: Parnas and Fruman began assisting Giuliani in efforts to unearth negative information in Ukraine about former Vice President Joe Biden, a candidate for the Democratic presidential nomination in 2020, and his son Hunter.

That work lies close to the center of the investigation by House Democrats of whether Trump oversaw a shadow diplomatic campaign intended to smear a political opponent.