RIO DE JANEIRO  -- Five young black men were killed recently in a hail of police bullets in a poor Rio neighborhood  after celebrating a pay check that one of them -- a 16-year-old -- had earned in his first-ever job.

Such a killing would have raised an outcry had it occurred in the United States. Yet most Brazilians barely noticed. In a country where violent crime is a huge issue, few people seem prepared to challenge the police.

“It is as if nothing happened,” said Humberto Adami, director of Rio’s Institute of Racial and Environmental Advocacy, a legal group. “Why don’t people get as indignant as in the United States?”

Campaigners tried to mobilize outrage after  the killings. An anti-racism banner was raised at a Rio demonstration last week. Relatives and friends of the victims also held a small protest. On Tuesday, Amnesty International delivered a petition with 60,000 signatures protesting police killings to Rio’s governor, Luiz Pezão. Many Brazilians expressed their shock online.

But there was nothing on the scale of the outrage seen in the United States, where police killings of black men have touched off major protests and Justice Department investigations.

In both countries, blacks appear to be killed by police in numbers disproportionate to their share of the population. While there is little official U.S. data, The Washington Post has found that about a  quarter of people killed by U.S. police this year were black. In Brazil, a report by Amnesty International found that 79 percent of the victims of killings by on-duty police in Rio from 2010-13 were black or mixed race. A separate study, co-authored by Jacqueline Sinhoretto, a sociology professor and violence specialist at the Federal University of São Carlos in São Paulo state, found that 64 percent of those killed by police in the city of São Paulo in 2014 were black.

The recent case was particularly shocking. On Nov. 28, four black men -- Wilton Domingos Júnior, 20, Wesley Rodrigues, 25, Cleiton de Souza, 18, and Carlos de Souza, 16 (who is no relation) went to the Madureira Park in northern Rio to celebrate with Roberto de Penha, 16, who had just started work at a nearby supermarket.

When the five men's white Fiat  reached Costa Barros, the neighborhood where de Penha lived, they were met with a hail of police bullets. Four officers have been jailed in the case. They claimed they were fired at when they went to investigate a stolen truck in this notoriously violent area of Rio. Witnesses accused the officers of putting a gun into the hand of one of the dead men to fake signs of a shootout.

Authorities said the police officers involved will be tried. "It was a tragic and indefensible action," said Rio's state security secretary, Jose Beltrame.

And yet, the attack and its fallout have found little space in the national media, which are more focused on Brazil's political crisis and the start of impeachment proceedings against President Dilma Rousseff.

There are several possible explanations for the limited reaction.

One is that officials insisted that race was not a factor in the killings.

“It’s not racism,” said Rio state governor Luiz Pezão.

Many Brazilians seem inclined to believe that explanation. In part, that's because, unlike in the United States, blacks and mixed-race people are not a small minority. Slightly more than half of Brazilians identify themselves as black or mixed-race, compared to about  15 percent in the United States.

While the majority of American police officers are white, half of Brazil's police identified themselves as either black or mixed race in a 2014 study produced by the Brazilian Public Security Forum, a non-governmental group.

Meanwhile, murder rates are much higher in Brazil than in the United States, and many fearful citizens approve of an iron-fisted approach by police. In a survey carried out in July by the Datafolha Polling Institute, 50 percent of residents of big Brazilian cities said they agreed with the common expression "The only good bandit is a dead bandit."

Many see Brazil's justice system as slow and prone to errors, said Sinhoretto, the violence expert. "The logic in people's minds is that nothing works, let the police act," she said.

She added that while protest groups pressure the authorities about police killings, mainstream media do not. That makes is easier for the authorities to avoid proper investigations. And that, in turn, contributes to public apathy.

"In general, the inquiries into these denunciations will conclude that there was no crime, that there was a confrontation, shots, that it was legitimate defense," she said.

Amnesty found that of 220 investigations launched into homicides as a result of police action in 2011 in Rio, 183 cases were still open in April of this year and only one officer had been charged.

Brazilians may also be reluctant to protest abuses since so many fear the police -- 60 percent of people in São Paulo, according to a November Datafolha poll.

Jorge de Penha, 50,  father of Roberto, said that racism was indeed a factor in the killing of his son and his friends. In Rio’s richer, whiter "South Zone," which is home to beach neighborhoods like Ipanema, police would have stopped the car to see who was in it, he said. In the poorer, blacker "North Zone," where he lives, they just opened fire, he said.

“This makes me angry,” said de Penha, a welder who has been studying law.

His son was a happy teenager who liked to design on a computer, he said, not a member of one of the armed drug gangs that operate in many Rio slums.

“He was a wonderful boy,” said de Penha.