Bob Costello, attorney who advised Michael Cohen, testifies for defense in Trump grand jury probe

Bob Costello, an attorney who previously advised former Trump lawyer Michael Cohen, told reporters his former client has a "lie, cheat, steal" mindset after Costello testified for the defense Monday before the Manhattan grand jury investigating former President Donald Trump's role in the hush payment to adult film actress Stormy Daniels.

Costello, a longtime Trump ally, appeared before the grand jury as an exculpatory witness after Trump's legal team asked the DA to allow him to testify, according to a letter to prosecutors obtained by ABC News.

Cohen, Trump's former personal attorney, paid $130,000 to Daniels in the closing days of the 2016 presidential campaign to allegedly keep her quiet about an affair she claimed to have had with Trump. The former president has denied the affair and his attorneys have framed the funds as an extortion payment.

Manhattan District Attorney Alvin Bragg is mulling whether to charge Trump with falsifying business records, after the Trump Organization allegedly reimbursed Cohen for the payment then logged the reimbursement as a legal expense, sources have told ABC News. Trump has called the payment "a private contract between two parties" and has denied all wrongdoing.

Speaking to reporters after his grand jury appearance, Costello painted Cohen as an unreliable witness on which to base an indictment of the former president.

"I'm trying to tell the truth to the grand jury," Costello said. "If they want to go after Donald Trump and they have solid evidence, then so be it. Michael Cohen is not solid evidence."

Costello testified for about two and a half hours, during which he said he described an initial meeting with Cohen during which Cohen was "talking to us while pacing like a wild tiger" and vowing "to do whatever the f--- it takes" to avoid prison.

"He went to jail," Costello said of Cohen, who served prison time after pleading guilty to federal charges related to the hush payment. "Now he's on the revenge tour."

Cohen has said previously that "this is not about revenge," but about telling the truth.

Cohen was present Monday at the district attorney's office to be available as a rebuttal witness, but he did not testify.

Trump wrote on social media Saturday that he was expecting to be arrested Tuesday, and called on followers to protest.

New York City Mayor Eric Adams said Monday that the city is prepared for any protests related to a potential indictment.

"We are monitoring comments on social media, and the NYPD is doing their normal role of making sure there is no inappropriate actions in the city," Adams said.

ABC News' Katherine Faulders contributed to this report.