Philando Castile was shot in his car in St Paul, Minnesota, on Wednesday as he reached for his driving licence, his girlfriend said in a Facebook Live video taken during the aftermath.
His death follows that of Alton Sterling, who was shot dead by police during an incident in Baton Rouge, Louisiana, on Tuesday.
What do we know about the two victims?
The 32-year-old had worked in the canteen of a school in St Paul for more than 10 years, his uncle Clarence told media in Minnesota. The JJ Hill Montessori Magnet School in the city listed Mr Castile as a cafeteria supervisor on its website.
On his Facebook page, Clarence later re-posted comments by a Minnesota bishop, Divar Kemp, calling Philando Castile "an a1 genuine man who was killed because he obeyed what the officer asked him".
Mr Castile's cousin, Antonio Johnson, told the Star Tribune newspaper his cousin had graduated with honours from St Paul Central High School.
Mr Castile was "a black individual driving in Falcon Heights who was immediately criminally profiled and he lost his life over it tonight", he said.
He added that Mr Castile was "very non-confrontational" and "a real upstanding citizen".
The Star Tribune said Mr Castile had only minor offences on his criminal record.
Little is publicly known about Mr Sterling, 37.
The father of five sold CDs and DVDs in the car park in which he died, family members told media in Louisiana.
"If you asked Alton for the shirt off his back, he'd give it to you," his aunt, Lorna, told The Advocate newspaper. "Alton would give you the world."
One broadcaster, 9News, said Mr Sterling had a long criminal record, that included several battery, drug, and burglary charges. It said he was also arrested in 2009 for resisting an officer and illegally carrying a weapon.
But Lorna Sterling said her brother had sought to earn a living after his last conviction in 2011.

The hospital said additional beds had been opened to relieve the pressure on the A&E department.
A spokesperson for Belfast Trust said the situation was brought under control just before midnight on Wednesday.
The RVH said anyone attending A&E could still expect to wait longer than normal.
Earlier on Wednesday evening, ambulances were diverted to the Ulster Hospital in Dundonald for several hours, but they are now returning to the RVH.
The hospital said some patients may still be transferred to other sites.
A spokesperson for the Belfast Trust said "everything that could be done, had being done".
She described it as a "very unusual situation".

James Isbister caught the 6ft-long ling while fishing off Muckle Flugga on Saturday.
Mr Isbister is awaiting confirmation from the relevant authorities of its possible record-breaking status.
The fish is currently being kept in his mother's freezer. "It was a very big fight," he said.
He said he would keep trying to catch an even larger fish.
He told BBC Scotland: "Muckle Flugga is renowned for big fish.
"It took about 20 or 30 minutes.
"I knew it was a big fish but I didn't realise it was that size - I am 6ft 5in and it's as big as me."
Mr Isbister added: "It's in my mum's freezer. We had to make room for it, it fills the whole freezer.
"I am a local celebrity at the moment."

Four men wearing masks entered the property on the Boleran Road in Garvagh about 20:00 BST on Thursday.
Two of the men, armed with a screwdriver and poker, held the couple in the kitchen while the others ransacked the house.
The gang left a short time later but police said it was unclear at this stage if anything was taken.
The couple, a man in his 90s and a woman in her 70s, were not physically harmed during the incident, but were treated for shock.
Police have appealed for anyone who saw a white coloured pick-up type vehicle being driven on the Boleran Road or in the general Garvagh area on Thursday to contact them.
DUP MLA for East Londonderry, Adrian McQuillan, said: "I totally condemn those responsible for this barbaric act of burglary and appeal to anyone with information to bring it forward to the PSNI."
Two black men have been shot dead by police in the US this week, the latest in a line of similar incidents, many of which have led to protests.
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The Royal Victoria Hospital (RVH) in Belfast has called in extra staff to deal with an unusually high volume of patients.
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A Shetland fisherman is celebrating after reeling in a giant fish weighing more than 67lbs (30kg).
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An elderly couple have been held by a gang armed with a poker at their home in County Londonderry.