More than 500 former federal prosecutors on Monday signed a letter saying President Donald Trump would have been charged with obstruction based on the allegations in special counsel Robert Mueller’s report if he were not occupying the Oval Office.

One notable exception: former New York Mayor Rudy Giuliani, a former federal prosecutor who is now a personal attorney to Trump.

Jeffrey Harris, one of the signatories, told CNN he had worked with Giuliani on a daily basis for nearly five years, including as his principal assistant. And he says his old boss would’ve charged Trump based on the Mueller report’s evidence:

“I have absolutely no doubt that the prosecutor Rudy Giuliani would have indicted someone who committed the acts that are put out in the Mueller report in a heartbeat. I am 100% confident of that.”

Giuliani dismissed the criticism, telling Politico that Harris is a Democrat and that none of the letter’s signatories are Trump supporters.