Police officers stand guard at Rio de Janeiro's Alemao favela on April 4, 2015
Rio de Janeiro (AFP) - Police in Rio de Janeiro state, which hosts next month's Olympics, killed at least 645 people last year and 8,000 over the last decade, a rights group said Thursday.
The toll includes dozens of execution-style killings in addition to the lethal violence used during standard police work in the state, the report from Human Rights Watch said.
The international rights group identified 64 cases in the last eight years in which Rio police allegedly tried to cover up extrajudicial killings of 116 people, including at least 24 minors.
"Killing criminals was a requirement from my superiors as a way of showing that we were performing well," one of 30 police officers interviewed for Human Rights Watch's study alleged.
The officer said he had been stationed in one of Rio's most dangerous neighborhoods where he took part in operations against heavily armed drug traffickers. The strategy was to kill them as a way to reduce crime, he said.
The officer, who is still on the force, spoke on condition of anonymity for fear of reprisals.
He was quoted as saying that some police would capture suspected drug traffickers and kill them, sometimes to gain status as killers and to boost their own extortion rackets.
They would sometimes plant weapons or drugs on the corpses and intimidate witnesses, the report said.
It cited prosecutors as saying that in 2011 police tortured and killed the 14-year-old son of a woman who witnessed an execution.
The pressure to play along makes honest policing difficult in Rio.
"Illegal executions by police colleagues turn an already dangerous job into something even more dangerous" and stoke anger against the authorities, the report said.
- Who's to blame? -
Rio state's prosecutor general, Marfan Martins Vieira, told Human Rights Watch that a large proportion of shoot-outs reported by police are staged.
However, he said that his office had only taken on "a very small number" of cases involving murder by police.
Vieira accused the Civil Police, which investigate homicides, of not fulfilling their task, but Human Rights Watch says the ultimate responsibility lies with prosecutors.
Only eight of the 64 cases investigated by Human Rights Watch have gone to trial and only four of those resulted in prison terms for police.
"Responsibility for putting an end to the impunity of recent times rests with the office of the prosecutor general of Rio de Janeiro, who has legal authority to supervise the work of police investigators, as well as to run its own investigations," the report said.
The findings come less than a month before Rio becomes the first South American city to put on the Olympic Games.
Security has become a major concern in the run-up, with the authorities drafting in soldiers and extra police to build up an Olympic security force of 85,000 people -- double the number used in the 2012 London Olympics.
Criticized over rising crime rates, police say their job has become too dangerous, with more than 50 officers killed in Rio state just this year.
Police in Rio are also angry over months of unpaid overtime and late salary payments. Emergency government funding was due to reimburse the police this week.
Police killed 24 civilians for every officer that died on duty in 2015. The ratio was twice that of South Africa and three times that of the United States.
Abuses by police undermine their efforts to bring order to Brazil's violent slums or favelas, HRW warned.
"If there are police officers killing members of the community, how are we going to have community policing?" said Cesar Munoz, the chief HRW researcher behind the report.