New York City Mayor Bill de Blasio was confronted with “Fire Pantaleo” chants during his opening statements at the second night of the Democratic debate on Tuesday, in reference to Daniel Pantaleo, the NYPD officer who put Eric Garner in a lethal chokehold in 2014 and remains on the force.

While de Blasio was able to plow through the chants, the protesters started again when Sen. Corey Booker (D-NJ) began speaking, prompting him to pause and wait until the crowd grew quiet.

De Blasio has faced mounting calls to take action against Pantaleo after the Justice Department announced earlier this month that it would not bring federal charges against the officer, whom a Staten Island grand jury declined to charge in 2014. Pantaleo remains on the force despite a medical examiner testifying that Garner’s death in police custody was a homicide.

After initially sending out a tweet telling the protesters he had “heard” them from the debate stage (“I thank you. This is what democracy looks like and no one said it was pretty”) de Blasio was asked later in the debate to comment on the issue.

The New York City mayor promised that the “Garner family is going to get justice in the next 30 days” but stopped short of offering to take any concrete steps.

“We are not waiting for the Justice Department,” he said, adding that he was working on “making sure there will never be another tragedy, there will never be another Eric Garner.”

Pantaleo faced an internal disciplinary hearing earlier this month and an administrative judge has yet to recommend whether to sanction Pantaleo. The final decision will be made by NYPD Commissioner James P. O’Neill.

De Blasio has repeatedly suggested that he has no power to take action against Pantaleo, initially leaving the NYPD officer’s fate up to the Justice Department. But Pantaleo’s administrative trial began weeks before the federal decision, after the mayor said it had been a mistake to wait four years for the feds.

“It’s not my place to pass judgment,” de Blasio said in May, stressing that the decision would ultimately be made by the police commissioner who answers to him, and that he had no direct power to fire the officer and didn’t want to interfere with due process.

Booker criticized the Justice Department’s decision not to prosecute, writing in a letter to Attorney General William Barr that Pantaleo’s use of force while arresting Garner for allegedly selling untaxed cigarettes was “deeply alarming” and calling the response from the DOJ “disappointing.”

“It’s why many people—particularly people of color—feel as if the system is stacked against them without hope of accountability, even when a violent and unnecessary homicide is captured on video, for all the world to see,” Booker wrote, according to The Hill.

He also reportedly called the department’s decision “a larger pattern of the Attorney General abdicating his responsibility to uphold the law” in a statement.

Minutes after the chanters had interrupted his opening statement, Booker’s account tweeted:

“To the folks who were standing up to Mayor de Blasio a few minutes ago—good for you. That's how change is made.”