Philadelphia will deploy more police officers and has called for help from the National Guard as it braces for further unrest after the police killing of a Black man armed with a knife, authorities said on Tuesday.
Hundreds of protesters took to Philadelphia's streets on Monday after a bystander's video was shared on social media showing two officers shooting 27-year-old Walter Wallace after he did not heed orders to back off and to drop the knife.
Wallace was bipolar and his mental issues were relayed to the officers before the shooting, a lawyer for the family said.
While the demonstrations began peacefully on Monday at Malcolm X Park on the west side of the city, they later turned violent, inflicting significant damage on businesses and leading to 91 arrests, commissioner Danielle Outlaw told a briefing.
"For today and this evening we anticipate the chance of additional incidents of civil unrest and as such we will be taking additional steps to ensure order," Outlaw said, adding that she had asked surrounding counties for assistance.
Later, the office of Philadelphia Mayor Jim Kenney said the Pennsylvania National Guard had been called on to help deal with the unrest.
Philadelphia was one flashpoint in a summer of anti-racism protests across the United States set off by the May 25 death of George Floyd, an African-American man who died after a white Minneapolis police officer knelt on his neck for nine minutes.
The protests, and law enforcement response to them, have been an issue in the race for the White House between Republican President Donald Trump and his Democratic Party challenger Joe Biden.
"Our hearts are broken for the family of Walter Wallace Jr., and for all those suffering the emotional weight of learning about another Black life in America lost," Biden and running mate Kamala Harris said in a statement on Tuesday.
"We cannot accept that in this country a mental health crisis ends in death."
Kenney said the video of the shooting presented "difficult questions" about the actions of the officers. "Last night we saw further evidence of the anguish of Black and Brown residents of our city who have struggled their entire lives under systemic racism," he told the briefing.
But he also expressed sympathy for the officers injured in the protests and for the business owners whose shops were damaged, saying the law would be enforced.
"Vandalism and looting is not an acceptable form of First Amendment expression," Kenney said, referring to the constitutional amendment guaranteeing freedom of speech.
Outlaw said a total of 91 arrests had been made, including 11 for assaulting officers and 76 for burglaries. Of the 30 officers injured, 29 were in stable condition, mainly after being hit by bricks and other projectiles. One officer, run over by a truck, was being treated in a hospital, Outlaw said.
The bystander's video showed Wallace approaching two police officers who drew their guns after warning him to put down the knife. The video shows the officers backing up, then cuts briefly from view as gunfire erupts and Wallace collapses.
Chief Inspector Frank Vanore said the police had responded to a call about a man screaming who was armed with a knife, and that each officer fired about seven rounds. But he declined to go into further detail, citing the ongoing investigation.
John McNesby, the president of the Fraternal Order of Police Lodge #5, defended the officers in a statement.
"The use of lethal force is a very difficult decision and we support our officers as they worked to resolve this incident under a great deal of stress. These officers were aggressively approached by a man wielding a knife," he said.
Shaka Johnson, a lawyer for Wallace's family, told the Philadelphia affiliate of Fox TV that Wallace's wife had told the officers about his bipolar condition prior to the shooting.