The authorities say it is mainly criminals caught in military-style raids on drug gangs but according to a former senior official, new evidence suggests that many of the shootings are cold-blooded executions conducted by the police.

Former police ombudsman Professor Julita Lemgruber has told BBC World Service's Assignment programme that, in the state of Rio alone, the police killed 983 people last year. The figure is similar for Sao Paulo.

"The federal government should be challenging the various state governments in Brazil about the hundreds of people that the police kill in this country," she says.

Victims

As a former ombudsman, Professor Lemgruber was responsible for investigating the police as part of a previous crack down on corruption.

In the past five years, the number of fatal police shootings has more than doubled. Based on her experience as a government official, Professor Lemgruber says she believes the police are free to act with impunity.

"You couldn't really investigate complaints because you knew there was this curtain of silence that was always present," she says.

She adds that she had personally dealt with cases in which summary executions had happened.

The authorities in Rio dismiss these allegations. They say most people killed by the police are criminals, shot in military-style raids.

But in the spring of this year events took a sinister turn when, on 31 March, two men entered a bar and started shooting, not once or twice, but again and again. Most of the victims were shot at close range - in the chest and in the head.

In all, 29 people were shot dead, apparently not by members of a criminal drug gang - but by off-duty police officers.

Executions

A former military policeman, Gordinho (not his real name), says executions by police death squads are common.

"Everyone knows the police here in Rio de Janeiro... nearly all of them abuse their authority," he says.

Most people killed by police are criminals caught up in raids, officials say

"When you get excited you feel you are the law... The shooting cases you hear about, most of them are executions.

"It's all premeditated - very cold-blooded and calculated."

After the killings in March, Marcello Itagebah, Secretary of State for Public Security and the man ultimately responsible for policing in Rio, promised to take a "meat cleaver" to police corruption. Following the investigation, 11 police officers were arrested.

"That shows to the people that we can conduct a very good investigation and that we can arrest police officers that committed crime," he said.

"We already have arrested more than 500 police officers, and we have expelled about 200 since last February. That is a job that has to be done every day."

But executions by death squads appear to be a traditional feature of Rio policing. While the authorities no longer give them official backing, evidence from the city morgues suggests they continue.

"Around 60% of the bodies of people that were killed by the police had more than six shots," explains Professor Lemgruber.

"Most of them [were shot] in the head and in the back - mostly executions."

Brazil is a deeply religious nation. Leaders of the Catholic Church have spoken out against corruption in politics and in the police force.

And among the congregations in the favelas, there is growing anger. They are determined to fight for change.

"You see children playing in the streets, and the people all happy - but when the cops come here - pop pop pop - some people are killed," says one resident, Paolo Cesar.

"They kill everybody. They got bad cops - bad cops."

Another resident insists that "we are fighting really hard for justice because the guilty people have to pay".