Days before the election, the US is reminded of the unrest that spread through cities months ago forcing a national conversation on police accountability.
Protesters have returned to the streets, this time in Philadelphia, after police shot and killed an African-American man, 27.
Demonstrations have been held nightly since Walter Wallace Jr was killed on Monday.
A citywide curfew was introduced on Wednesday night, from 9pm to 6am, after looting, property destruction and increasingly violent confrontations between police and protesters.
Protests erupted on Tuesday night, with 91 people arrested, including 11 on charges of assaulting police and 76 for burglary.
Philadelphia Police Commissioner Danielle Outlaw said 23 police officers were injured.
Protests turn violent after black man is shot dead by police in Philadelphia
Tension rose again on Wednesday when the authorities found a van filled with explosives, propane tanks and torches.
It is unclear who the owner or operator of the vehicle is but the bomb squad was brought in to investigate.
The city has had an increase in ATM thefts this year, in which people use low-grade explosives to vandalise or steal the bank machines.
Philadelphia police said that nine ATM machines had been blown this week.
Mayor Jim Kenney said Pennsylvania National Guard troops would arrive in Philadelphia on Friday to assist the police.
“Their role, first and foremost, will be to safeguard property and prevent looting," Mr Kenney said.
"They will also provide assistance for our police department and other operational departments as needed."
The police body camera footage of the Wallace's shooting is expected to be released in the coming days.
His family viewed all available footage and listened to the 911 call on Thursday.
A GoFundMe page created by his family says Wallace was a father of seven, with another on the way, and was married only weeks ago.
Police say two officers responded to a call on Monday about a man with a knife.
“He was brandishing it and waving it erratically," Philadelphia Police Sgt Eric Gripp told KYW.
Grainy mobile phone footage captured the incident, in which Wallace is approached by officers, but the final moments before officers fired their guns were not captured.
His mother Cathy said the family called police for an ambulance as Wallace was in the middle of a mental health crisis.
She said officers had been to their house three times that day responding to the mental health calls.
The killing has reignited activists' calls for police reforms.
Democratic presidential hopeful Joe Biden has embraced the idea of social workers accompanying police officers to reports involving mental health issues.
