MINNEAPOLIS (AP) — Prosecutors charged three more police officers Wednesday in the death of George Floyd and filed a new, tougher charge against the officer at the center of the case, delivering a victory to protesters who have filled the streets from coast to coast to fight police brutality and racial injustice.

The most serious charge was filed against Derek Chauvin, who was caught on video pressing his knee to Floyd’s neck and now must defend himself against an accusation of second-degree murder. The three other officers at the scene were charged for the first time with aiding and abetting second-degree murder and second-degree manslaughter.

All four were fired last week. If convicted, they could be sentenced to up to four decades in prison.

Chauvin was initially charged with third-degree murder and second-degree manslaughter. Those charges still stand.

The new second-degree murder charge alleges that Chauvin caused Floyd’s death without intent while committing another felony, namely third-degree assault. It carries a maximum penalty of 40 years in prison, compared with a maximum of 25 years for third-degree murder.

The other officers — Thomas Lane, J. Kueng and Tou Thao — face the same maximum penalties for aiding and abetting.

The additional charges were sought by Minnesota Attorney General Keith Ellison, who called the protests unleashed by the death “dramatic and necessary” and said Floyd “should be here and he is not.”

“His life had value, and we will seek justice,” said Ellison, who cautioned that winning convictions would be hard and said that public pressure had no bearing on his decisions.

Hundreds of protesters were in New York City’s Washington Square Park when the charges were announced.

“It’s not enough,” protester Jonathan Roldan said, insisting all four officers should have been charged from the start. “Right now, we’re still marching because it’s not enough that they got arrested. There needs to be systematic change.”

Ben Crump, an attorney for Floyd’s family, called it “a bittersweet moment” and “a significant step forward on the road to justice.” Crump said Elison had told the family he would continue his investigation into Floyd’s death and upgrade the charge to first-degree murder if warranted.

The move by prosecutors punctuated an unprecedented week in modern American history, in which largely peaceful protests took place in communities of all sizes but were rocked by bouts of violence, including deadly attacks on officers, rampant thefts and arson in some places.

Some of the rockiness of the days since Floyd’s May 25 death dissipated on Tuesday night, with demonstrations continuing around the country, but without major reports of violence.

Curfews and efforts by protesters to contain earlier flare-ups of lawlessness were credited with preventing more widespread damage to businesses in New York and other cities overnight.

“Last night we took a step forward in moving out of this difficult period we’ve had the last few days and moving to a better time,” New York Mayor Bill de Blasio said.

New York police said about 280 people were arrested on protest-related charges Tuesday night, compared with 700 a day earlier. Nationwide, more than 9,000 have been arrested in connection with unrest.

At least 12 deaths have been reported, though the circumstances in many cases are still being sorted out.

Some tense incidents continued Tuesday night, but were far less prevalent than in preceding days. Police and National Guard troops used tear gas, flash-bang grenades, nonlethal rounds and other means of dispersing crowds near a police precinct in Seattle, near Centennial Park in Atlanta and at demonstrations in Tampa and St. Petersburg, Florida.

Minnesota has opened a civil rights investigation into whether the Minneapolis Police Department has a pattern of discrimination against minorities.