“Our mission is to protect life, preserve property and the right to peacefully demonstrate,” the Minnesota National Guard tweeted. “A key objective is to ensure fire departments are able to respond to calls.”

Angry crowds have gathered in cities nationwide to demand justice after the death of George Floyd following his arrest Monday over a counterfeit bill. The outrage grew after a video emerged showing a Minneapolis police officer kneeling on his neck during the arrest. He was unarmed and handcuffed, and cried that he couldn’t breathe before he died later.

In Minneapolis, buildings were burned, stores looted and a police precinct set ablaze Thursday night. Smoke and orange flames filled the night sky as people gathered nearby and shot video on their phones.

The Minneapolis Police Department has fired the four officers involved in Floyd’s arrest.

The incident is being investigated by local, state and federal authorities, and prosecutors urged residents to be patient.

“We need to wade through all of that evidence and come to a meaningful decision and we are doing that to the best of our ability,” Hennepin County Attorney Michael Freeman said.

Federal prosecutor Erica MacDonald told reporters that the priority is ensuring justice is served.

“We are going to investigate it as expeditiously, as thoroughly as justice demands,” Freeman said. “That video is graphic, horrific and terrible. And no person should do that. I am pleading with individuals to remain calm and let us conduct this investigation.”

All four officers involved in the death have invoked their Fifth Amendment right against self incrimination, Freeman told CNN following the news conference.

“I am absolutely sorry for the pain, devastation and trauma Mr. Floyd’s death has left on his family, his loved ones, Minneapolis and the world,” Minneapolis Police Chief Medaria Arradondo said.

The latest on the George Floyd case

“I know there is currently a deficit of hope in our city … and I know our department has contributed to that deficit as a whole.”

In Minneapolis, protests transitioned to rioting and looting south of downtown, with people smashing their way into stores and setting businesses and other buildings ablaze. There was more looting Thursday in St. Paul, the state capital, next door.

“I want everybody to be peaceful right now, but people are torn and hurt, because they’re tired of seeing black men die,” said Philonise Floyd, the victim’s brother.

Protesters have gathered in other cities too, including Denver and New York.

CNN’s Sara Sidner and Steve Almasy contributed to this report.