By Gary Duffy
BBC News, Sao Paulo
Prosecutors in the Brazilian city of Rio de Janeiro are seeking the arrest of 30 police officers who are suspected of killing innocent civilians.
The arrests were requested after an investigation into the deaths of 20 men and teenagers.
All of them were killed during police operations which were meant to be targeting crime.
One public prosecutor said the evidence pointed to activity that was typical of a "death squad".
Brazil's TV Globo described the request for the arrest of so many police officers as "unprecedented", but whether the case goes ahead will have to be decided by the judiciary.
All of the deaths involved so called "acts of resistance" a term used by police in Rio de Janeiro to describe the killing of suspects during an armed confrontation.
According to TV Globo, in the last six years there were on average three incidents a day of this kind and the sheer volume of cases prompted state public prosecutors to investigate.
Of just 20 deaths which they examined in the last two years all of the victims were teenagers or men aged between 14 and 29, and only two had police records.
It is reported that forensic tests show they all died after being shot at close range or in the back.
The request for 30 policemen to be arrested will now be considered by the judiciary, and the police in Rio say they are ready to give an explanation of all actions carried out by individual officers.
However speaking on TV Globo, a public prosecutor said the killings amounted to activity that was typical of a death squad.
He said specialist reports contradicted the police version of events that there had been a confrontation, and was evidence that those who died had been victims of summary executions.
In a report last year, the UN concluded that police in Rio de Janeiro routinely resort to deadly force and that a large number of off-duty officers take part in death squads and other forms of organised crime.
The report found that police are rarely punished for involvement in killings, so human rights groups will be watching carefully to see if the request for the arrest of so many officers indicates a shift in attitude by the authorities.