A short clip showed one guard restraining Joao Alberto Silveira Freitas just outside the doors of a Carrefour supermarket while the other pummelled him with repeated blows to the face.
Dozens of protesters entered a Carrefour in Brazil’s capital, Brasilia, on Friday morning, chanting “black lives matter”.
One held a sign reading: “Don’t shop at Carrefour. You could die.” Inside another Carrefour in Rio de Janeiro, protesters shouted “Carrefour killer” as a black man lay still atop the conveyor belt of a checkout.
In Sao Paulo, protesters smashed the front window of a Carrefour, scattered goods from shelves all over the store’s floor and set a fire that employees hurried to extinguish.
Carrefour released a statement lamenting Mr Freitas’ “brutal death”, and said it will end its contract with the security company, fire the store manager who was on duty and close the Porto Alegre store out of respect for the victim.
The men who beat Mr Freitas have been detained and are being investigated for homicide due to the victim’s asphyxiation and his inability to defend himself, said Nadine Anflor, the civil police chief for the southern state of Rio Grande do Sul, where Porto Alegre is the capital.
One of the men was a temporary military police officer who was off-duty, said Rodrigo Mohr, head of the state’s military police.
The two spoke on a Twitter video posted by governor Eduardo Leite, who highlighted recent state policies enacted to combat racial intolerance.
He said: “Unfortunately, on this day in which we should be celebrating those public policies, we come across scenes that leaves us all indignant due to the excessive violence that caused the death of a black citizen at the supermarket.”
Black Consciousness Day is observed as a holiday in many parts of Brazil.
In Rio on Friday, a group of people participated in a celebration with Afro-Brazilian dance and music in the working-class Santa Marta favela. Members of a samba school performed a ritualistic “washing” of the steps leading up into the hillside neighbourhood.
Black and mixed-race people account for about 57% of Brazil’s population but constitute 74% of victims of lethal violence, according to the Brazilian Forum on Public Safety, a nongovernmental organisation.
The percentage is even higher, 79%, for those killed by police.
Local online news site G1 reported that the incident at the Carrefour in Porto Alegre followed a confrontation between Mr Freitas and a supermarket employee, who then called security. Both guards were white, G1 reported.
After the death of George Floyd earlier this year in the US, Black Lives Matter protests drew hundreds of thousands to the streets around the world.
Racism doesn’t exist in Brazil. That is something they want to import here
They resonated in Brazil, too, where demonstrators turned out to demand justice for a 14-year-old boy killed by police in Rio de Janeiro.
Protesters in Brasilia also gathered on Friday outside a governmental institution that promotes black culture to denounce its chief, Sergio Camargo.
Mr Camargo, who is black, has denied the existence of structural racism in Brazilian society and called the Black Lives Matter movement “lefty garbage.”
Speaking to reporters, vice president Hamilton Mourao lamented the incident at Carrefour, but denied it reflected racism.
“Racism doesn’t exist in Brazil. That is something they want to import here,” Mr Mourao said. ″I lived in the United States. There is racism there.”