NEW YORK - A lawyer said he tried Monday to tell a grand jury weighing possible criminal charges against former President Donald Trump about evidence he thinks would undercut a key witness in the case, but was stymied by prosecutors - another strange twist in a seven-year legal saga that now has Trump on the precipice of an indictment.

The grand jury appearance of Robert Costello, a veteran New York City attorney who once served as a legal adviser to former Trump lawyer Michael Cohen, marked a long shot 11th-hour bid to prevent what would be the first indictment of a former U.S. president.

Costello emphasized he was not representing Trump, but wanted to share what he said were fatal flaws in Cohen's account of paying hush money in 2016 to Stormy Daniels, a porn star who claimed she had an affair with Trump.

In public statements, Cohen has said he arranged to make the payments himself to protect Trump's reputation and to avoid the money being traced back to the campaign. He was later reimbursed by Trump's business. Cohen's testimony is believed to be a key part of Manhattan District Attorney Alvin Bragg's investigation into whether to indict Trump on a false business records charge - one likely to be predicated on the accusation that the false record was filed to cover up another crime, in this case, a campaign finance violation.

After leaving the grand jury Monday, Costello spoke at length to reporters about how he tried to paint Cohen's testimony as problematic, noting that while federal prosecutors wrung a guilty plea from Cohen for multiple crimes and sent him to prison, they never used him as a witness in other criminal prosecutions.

"There's a reason for that - he's totally unreliable," Costello added.

Cohen, in turn, issued a statement saying: "If Bob Costello's comments were any more fantastical, he would be a bestselling fiction author. ... I stated years ago and remain consistent that the payment was done at the direction of, in coordination with and for the benefit of Donald J. Trump."

Costello said he gave the district attorney's office copies of more than 300 emails that he claimed would show Cohen's credibility problems. But the prosecutors who called him into the jury room only asked him about six emails, he said, and "took them out of context." The emails were from 2018 and 2019, Costello said, when Cohen was under investigation by federal prosecutors and Costello was advising him.

"I said: 'There's 321 emails, you need to see each and every email, which follow in chronological fashion and give you the life history of Michael Cohen dealing with our firm,'" Costello told reporters.

Grand jury proceedings are not public, and Bragg's office has declined to discuss details of the investigation.

It's highly unusual for a lawyer to provide evidence against someone they consulted with on legal issues, but Costello said he did so previously because Cohen had waived his attorney-client privilege - which Costello on Monday called "a very stupid move" by Cohen.

In a separate written statement, Costello described why he thought Cohen's account of the Trump hush money payments was contradicted by statements Cohen made to him in 2018, shortly after FBI agents raided his office searching for evidence.

Costello said in those conversations - in addition to saying he arranged the hush money payments to protect Trump's reputation - Cohen claimed that he didn't know of any crimes Trump had committed.

To defense lawyers and Trump's advocates, that is a critical distinction, and one which could torpedo the prosecution's premise.

The precise nature of the prosecutors' theory has not been made public, but according to people familiar with the case, they have been gathering evidence to show that the hush money payments amounted to an undisclosed campaign donation for Trump.

Years ago, federal prosecutors considered that and ultimately did not file charges against Trump - though they did accept a guilty plea from Cohen for arranging the payment.

Some lawyers have questioned whether it would be wise to charge Trump with a crime stemming from the payments, particularly given the outcome of a past case against John Edwards, the 2008 Democratic presidential candidate who beat criminal charges that hush money used to hide an extramarital affair amounted to illegal campaign contributions.

A jury acquitted Edwards case on one count and deadlocked on five other charges. Prosecutors had argued that nearly $1 million paid by two wealthy Edwards benefactors to keep his affair quiet was, in effect, illegal - while Edwards's lawyers argued the hush money was meant to spare Edwards's ailing wife any more pain and embarrassment.

Some campaign finance lawyers have argued that the lesson of the Edwards case is that it is difficult to win a conviction on such a case if one can reasonably argue that the hush money was paid at least in part to prevent private pain or reputational harm. Trump, they say, could theoretically argue that at the time the 2016 hush money payments were made to Daniels and another woman, he had to worry about damage to his image as a celebrity and reality TV star.

It is highly unusual - but not impossible - for grand jury witnesses such as Costello to convince a panel to reject charges pushed by a prosecutor. Costello has said his appearance was requested by Trump's lawyers, and it would have been legally risky for Bragg to ignore such a request. At the same time, New York defense attorney Xavier Donaldson said, the decision to do so reflected positively on the district attorney.

The move "should revolve any issues related to Bragg's integrity or commitment to fairness," Donaldson said.

Trump has publicly predicted he will soon be arrested, though there is no indication law enforcement officials have conveyed that to his lawyers, and it would be unusual for someone indicted of a relatively modest financial crime to not be allowed to self-surrender once the indictment is filed. But the courthouse activity and Trump's social media statements have led to a growing public expectation that the grand jury could vote in the coming days on whether to indict him.

Two law enforcement officials who have been briefed on security planning in the event of an indictment said they have been told to expect additional grand jury activity on Wednesday. If Trump were to be indicted on Wednesday, he most likely would not appear in court in New York until next week, said the officials, both of whom spoke on the condition of anonymity to discuss the planning.

News reporters greatly outnumbered about two dozen protesters who gathered Monday night at a pro-Trump rally organized by the New York Young Republican and Long Island Loud Majority clubs in a small park across the street from Bragg's office in lower Manhattan.

A small group of Chinese immigrants, several of whom spoke only Mandarin, had come from Long Island and Flushing, Queens, to make their displeasure known. "I'm a legal immigrant and I am sad to see this country go in the wrong direction, with the weaponization of the FBI and the district attorney," said Stephanie Lu, 55, a community health representative who said she fears America is being taken over by communists and wants to stop them.

Others, like military veteran Patrick Foley, 53, and his 15 year-old son Braxton, were tourists - in their case from greater Los Angeles.

Young Republicans President Gavin Wax, 29, said that if Trump is indicted, it will only increase his political power. "I think it only helps him because it makes him a martyr," Wax said. "As soon as the next polls come out, he'll probably be skyrocketing in the primary."

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Barrett reported from Washington. The Washington Post's Carol D. Leonnig in Washington and Jada Yuan in New York contributed to this report.