Philadelphia District Attorney Larry Krasner has fired 31 in the office as part of his promised shake-up of the city’s top law-enforcement agency.

The highly unusual mass firing Friday — his fourth day on the job — is part of Krasner’s mission of taking the office of 600 staffers in “a different direction,” said spokesman Ben Waxman. “Reorganization and a change in some key personnel are necessary to fulfill that promise.”

Former staffers said a number of those who were let go had taken the day off due to travel complications from lingering snow. Detectives from the office picked them up at their homes and brought them to the Center City office, where they were ushered into a conference room that became a tableau of anger and sadness. Some assistant district attorneys were sobbing silently. Others were crying loudly. Still others were just fuming.

Those fired include E. Marc Costanzo, Patrick Blessington, Jimmy Carpenter, John Delaney, Mark Gilson and Michael Barry. Some of them, including Delaney and Barry, were longtime veterans of the office.

Several of those fired did not return calls or declined comment.

Criminal defense lawyer Bill Brennan, who often tries cases against Philadelphia prosecutors, said he was “flabbergasted” by the news.

He said one of his clients is a defendant in an upcoming murder trial, and the prosecutor scheduled to try the case — and his supervisor — were both canned.

“I’m literally waiting for a call back from either of them,” Brennan said. “I don’t know who’s gonna call me back.”

Michael Meehan, who heads the Republican Party of Philadelphia, issued a statement that the firings “are what we might expect from a defense attorney who made a career out of suing the police. Krasner places victims on the back burner from day one.”

Many of the prosecutors who lost their jobs were well respected in the local criminal justice community, Brennan said.

“There’s a lot of names on that list of people I fought with in the courtroom for 30 years — but, off the battlefield, I have tremendous respect for, admiration, affection. I mean, these are good people,” he said. “I’ve never seen a mass firing like this in my 30 years of practicing. But I have to assume there’s some kind of plan here.”

Krasner, a maverick civil rights lawyer, campaigned on a platform of upending the DA’s office. It included backing policies such as reducing the jail population, ending cash bail and favoring second chances over harsh punishments for gun and drug offenders.

On the campaign trail, one of his mantras became, “we have to change the culture of the DA’s office.”

Waxman, the Krasner spokesman, said, “change is never easy, but DA Krasner was given a clear mandate from the voters for transformational change.”