President Donald Trump's longtime lawyer Michael Cohen has reportedly hired a new attorney named Guy Petrillo.

Petrillo used to be in charge of the criminal division in the US Attorney's Office for the Southern District of New York.

That's where Cohen is under criminal investigation.

Harvard law professor Alan Dershowitz told Business Insider this is "the kind of lawyer you would hire if you wanted to keep open the option of cooperation."

Michael Cohen, President Donald Trump's longtime attorney, has reportedly hired his own new lawyer in relation to the criminal investigation surrounding him, Vanity Fair reported Tuesday.

Guy Petrillo, Cohen's new lawyer, is a partner at Petrillo Klein & Boxer. He served as the chief of the criminal division in the US Attorney's Office for the Southern District of New York from 2008 through 2009, and was an assistant US attorney in the office from 1990 through 1997. He did not immediately return a request for comment from Business Insider.

Cohen is under federal criminal investigation in the southern district for possible campaign-finance violations, bank fraud, wire fraud, illegal lobbying, and possible other crimes following the FBI's raids on his home, office, and hotel room in April.

The case currently centers on the documents obtained by the FBI as lawyers for Cohen, Trump, and the Trump Organization race to make declarations on what they believe should be covered by attorney-client privilege — and therefore not able to be used in a potential prosecution of Cohen.

Petrillo is 'the kind of lawyer you would hire if you wanted to keep open the option of cooperation'

Lynn Neils, a partner at Baker Botts and a former federal prosecutor with the Southern District of New York who knows Petrillo, told Business Insider that Petrillo knows the district "very well and will be independent."

"Works for his own firm so will not have the conflicts or have to worry about offending clients by taking on a controversial representation," she said. "Good choice on Cohen’s part."

Donald Trump. Alex Wong/Getty Images Another former federal prosecutor who knows Petrillo called him the "real deal," though he added that "he does not come cheap."

"It is possible that Guy Petrillo and his team have been brought in to try a major felony case," said the former federal prosecutor, who requested anonymity to speak freely about the proceedings. "That is in their wheelhouse, if they make it their primary focus. It is also possible that this group has been brought in to handle plea negotiations. That also is in their wheelhouse."

"If the Petrillo firm were to handle a major trial, I cannot imagine them charging less than seven figures – and in all likelihood north of $2 million," the person said. "They would want cash up front, or some other major guarantee that they would get paid."

Last week, multiple reports said Cohen was ditching his current legal team from the firm McDermott, Will, & Emery, which included attorneys Stephen Ryan, Joseph Evans, and Todd Harrison. The attorneys have not yet filed to US District Judge Kimba Wood a notice to withdraw from the case.

Some of the reports said the change made it likely that Cohen would cooperate with federal prosecutors in Manhattan, possibly even "flipping" on Trump and providing the government with damaging information on him.

Harvard law professor Alan Dershowitz told Business Insider on Tuesday that Petrillo is "the kind of lawyer you would hire if you wanted to keep open the option of cooperation."

Cohen's previous legal team specialized in document review. With that portion of the legal process currently wrapping up, Vanity Fair reported that Cohen would seek representation more familiar with the Southern District of New York.

The impending legal shakeup led to Trump facing questions recently about whether Cohen would cooperate or "flip."

Speaking to reporters outside the White House, Trump said he wasn't worried at all about such cooperation.

"I did nothing wrong," Trump said. "You have to understand, this stuff would've come out a long time ago. I did nothing wrong. I don't do anything wrong."

Trump added that he "always liked Michael," though he said he hasn't "spoken to Michael in a long time."