A Manhattan prosecutor who investigated Donald Trump’s financial dealings wrote in a resignation letter that he believed Trump “is guilty of numerous felony violations” and blasted the new district attorney for not moving ahead with an indictment, the New York Times reported.

Mark Pomerantz and Carey Dunne, two top prosecutors on the Manhattan district attorney’s criminal investigation of Trump, resigned abruptly last month, amid reports that the investigation into the former president’s finances was foundering.

The newly elected district attorney, Alvin Bragg, was reportedly more skeptical than his predecessor that the evidence his office’s attorneys had gathered against Trump would be enough to convict him.

In a February resignation letter obtained by the New York Times, Pomerantz wrote that the team of lawyers investigating Trump had “no doubt” he had “committed crimes” and that Bragg’s decision not to move ahead with prosecuting Trump “will doom any future prospects that Mr Trump will be prosecuted for the criminal conduct we have been investigating”.

“His financial statements were false, and he has a long history of fabricating information relating to his personal finances and lying about his assets to banks, the national media, counterparties, and many others, including the American people,” Pomerantz reportedly wrote.

The clock is ticking on the case against Trump, as the current term of the grand jury which has been hearing evidence expires in April.

Ronald Fischetti, an attorney for Trump, told the Guardian that the resignation letter simply reflected the prosecuting team’s failure to make a convincing legal case against the former president, describing his client’s “innocence”.

“Pomerantz had several occasions to meet with Alvin Bragg, the district attorney, and his senior staff to lay out exactly what he intended to present to the grand jury in order to get an indictment, and he failed,” Fischetti said. “He was unable to convince the DA and his senior staff that he had sufficient evidence to warrant an indictment.”

“Mr Bragg should be commended for not doing this on the basis of politics, and just doing it on the basis of law, which he’s supposed to do,” Fischetti said.

While the resignation letter conceded that the case against Trump could be challenging and that there were “risks” of bringing it to court, it argued that there was a strong public interest in prosecuting Trump “even if a conviction is not certain”.

The former Manhattan district attorney Cy Vance, who had been deeply involved in the case, had “directed the team to present evidence to a grand jury and to seek an indictment of Mr Trump and other defendants as soon as reasonably possible”, Pomerantz reportedly wrote, but Bragg, who was sworn in this January, reviewed the case and did not agree.

Pomerantz believed Bragg’s decision not to seek an indictment of Trump was “made in good faith” but also “misguided and completely contrary to the public interest”.

Pomerantz did not respond to a request for comment.

“The investigation continues,” Danielle Filson, a spokesperson for the district attorney, wrote in an email. “A team of experienced prosecutors is working every day to follow the facts and the law. There is nothing we can or should say at this juncture about an ongoing investigation.”

A spokesperson for the Trump Organization called Pomerantz a “never-Trumper” in a statement to the New York Times.