Philadelphia police killed a 27-year-old African American who wielded a knife in the street, sparking protests in which about thirty officers were injured, 10 people were arrested and several shops looted.
The victim was named Walter Wallace.
According to media reports, two policemen fired several shots at him Monday afternoon after he refused to drop the weapon while his mother tried to stop him.
His family now criticizes the use of lethal force.
Police Commissioner Danielle Outlaw has promised a full investigation into the killing of the African American in Philadelphia.
"I have ordered an investigation to be initiated, I recognize that the video of the incident raises many questions. The inhabitants have my assurance that those questions will be fully addressed by the investigation," he said.
Biden condemns African American killing 'but no violence' - "We cannot tolerate a mental health crisis in this country ending in death": so Joe Biden and Kamala Harris on the killing of Walter Wallace in Philadelphia by two agents , whose life, "like many others, was a black life that meant, for his mother, for his family, for his community, for all of us", they say, evoking the slogan of the Black Lives matter movement.
The ticket dem, however, warns that "no level of anger against real injustices in our society justifies the violence", as happened in Philadelphia.