The last time Juan Moraes' mother saw him alive, she asked the 11-year-old and his brother to run an errand. On their way back, her two boys ran into police gunfire.
The older boy, Wesley, 14, was hit in the shoulder and the leg. He saw Juan fall, bleeding, and crawled away for help. When he came back, Juan had vanished.
Investigators didn't visit the scene until a week later. By then, the only trace left of Juan was one lilac flip-flop, smeared with blood _ a sandal the child had borrowed from his mother. His body was found three days later, dumped in a river near police headquarters, 11 miles (18 kilometers) from where he was shot.
Even in a city where police shootings are routine, Juan's story touched a nerve. When he was missing, protesters held up posters asking "Where is Juan?" with a photo of the boy: striped shirt, round cheeks and big brown eyes. Now they're demanding justice, and officials are promising change.
The Brazilian city that will host the 2016 Olympic Games has one of the deadliest police forces on the planet. Efforts to bring the problem under control have so far produced only modest improvement.
In the last five years, officers in Rio have killed on average 3.5 people per day, according to an Associated Press analysis of police data. Just a decade ago the force gave cash bonuses to officers who killed suspects in firefights.
Since 2008, a new "pacification" program has established permanent posts in some slums and encouraged community-oriented policing. The killing rate dropped. In the state of Rio, police slayings fell from a high of 1,330 dead in 2007 to 854 in 2010. By comparison, police in the entire United States, with a population 20 times larger than Rio state's, killed 406 people in 2009.
Juan Moraes' case was an example of how serious the problem still is.
"According to our investigation, Juan died with a shot to the neck, and he was killed by police officers," said Ricardo Barbosa, chief of the homicide division of the regional police department, in a press conference this week, a month after the boy's death.
The four officers suspected in Juan's death were involved in 37 on-duty killings in total, according to police records. All the deaths were in the northern outskirts of Rio, where Juan's family lives.
Investigators say the bullet that killed Juan came from the assault rifle of 43-year-old Edilberto do Nascimento, who already had 13 so-called resistance killings to his name. The category, separate from homicides, is exclusively for suspects killed by on-duty police.
In 2008 Nascimento was charged with murder in a 14th death, but remained on his beat. He is also being investigated in another case involving a murder, a 15th death, and taking stolen property.
"There is a lack of investigation, of follow-up. There is a culture of impunity that leads to cases like Juan's," said Marcelo Freixo, head of the state legislature's human rights commission. "You have parts of Rio where the state has great interest, where there's investment of private capital, and things are changing there. But in other areas, the police haven't changed."
A state legislative report in 2007 showed that many of those killings appeared to be summary executions. In 83 percent of cases there were no witnesses willing to testify. Sixty-one percent of victims had at least one shot in the head and 65 percent had at least one shot in the back.
The United Nation's expert on extra-judicial executions, Phillip Alston, issued a report last year saying that "almost no steps have been taken to address the grave problem of on-duty police killings, or to reduce the high numbers of so-called 'resistance' killings."
Juan's murder has become a lightning rod for long-simmering indignation, said Ignacio Cano, a professor with Rio's state university who researches police violence.
"Police lost their moral standing with this case; it was clear no one was investigating anything," he said. "All this talk of pacification, and of preparing the city for the Olympics, contrasted too sharply with what happened."
On Thursday, the officers involved in the shooting were arrested. Investigators said witnesses had refused to cooperate in the case because they were afraid of retaliation. Juan's mother and brother, fearing for their lives, entered a witness protection program.
The head of Rio's military police, Mario Sergio Duarte, acknowledged the force's violent past, but insisted the police are changing.
"The context in which they worked was one of armed conflict," Duarte recently told the AP.
Between 2005 and 2010, 166 officers died on the job in Rio, according to police data. That's one officer dead for every 39 people killed by police.
"Under previous governments, it was the Wild West: you go to war, you're rewarded," Duarte said, referring to a state policy in the 1990s that gave officers promotions and cash bonuses for engaging alleged criminals in shootouts that resulted in death.
That policy has been canceled. Instead, there are financial incentives for lowering the number of resistance killings.
The public safety department also said that 947 officers have been kicked out of Rio's police force over the past four years for committing serious crimes, mostly murder. Starting this month, because of Juan's death, officers involved in a killing must surrender their weapons pending an investigation.
Duarte said deeper change will come as the pacification program spreads to other poor communities and citizens come to have higher expectations of their police.
So far, the 18 community policing units are islands of exception in the state's more than 1,000 slums. Most of the units are on Rio's wealthy south side, bordering brand-name neighborhoods like Ipanema or Copacabana, or near Maracana, the football stadium that will host the championship match of the 2014 World Cup.
Meanwhile, Juan's mother and brother have been moved out of the state, cut off from old friends and neighbors.
Juan was buried in a rushed ceremony that was closed to the public for what police said were safety reasons. His mother, brought back to Rio under heavy police escort for the funeral, cried as headlights from patrol cars lit the scene. It was all over in 10 minutes, according to the state department of social welfare and human rights, which paid for the burial.
Officers involved in the shooting had initially accused Wanderson Assis, a 19-year-old who took three bullets and saw Juan get shot, of being involved with drug trafficking. The teenager spent his days in the hospital handcuffed to the bed until public defenders were able to show he worked days at a candy shop to pay for night school.
Assis was escorted from the hospital straight into the protection of the witness program, along with his family.
"The lives of these families, of their neighbors, are shattered," Freixo said.
(This version CORRECTS Corrects that officers arrested Thursday, not Wednesday; minor edits throughout; removes extraneous wording in 21st paragraph; Adds photos.)