The report finds that on-duty police routinely resort to deadly violence and that a large number of off-duty police take part in death squads and other forms of organized crimes.
"In Rio de Janeiro, the police kill three people everyday," said Philip Alston, the UN Special Rapporteur on extrajudicial, summary or arbitrary executions.
"They are responsible for one out of every five killings," Mr. Alston added in a press statement announcing his report of a fact-finding mission last year in Brazil, where he met with Government officials, including police commanders and senior ministers, as well as non-governmental organizations (NGOs) and over 40 witnesses to human rights abuses.
Mr. Alston was especially critical of the "mega-operations" strategy involving hundreds of police assaulting gang-controlled neighborhoods, which is increasingly popular in Rio de Janeiro.
"Local officials claim that these impressive sounding mega-operations are protecting residents from drug gangs, but the operations have hurt ordinary people far more than they have hurt the drug gangs," Mr. Alston said.
A June 2007 operation in the impoverished Complexo do Alemão favela, near Rio de Janeiro, involved over 1,450 police and killed 19 people, but only resulted in the capture of two machine guns, six handguns, one sub-machine gun and 300 kilograms of drugs. Independent experts concluded that a number of the dead had most likely been summarily executed.
Mr. Alston reported that there has been little public outcry at police violence in Brazil because of widespread skepticism over normal law enforcement measures used to combat drug gangs.
"A remarkable number of police lead double lives," said Mr. Alston, "While on duty, they fight the drug gangs, but on their days off, they work as foot soldiers of organized crime."
Some 70% of homicides in the northeastern state of Pernambuco are committed by death squads, many of which are comprised of either current or former police officers. The squads are typically contracted to murder business, political or personal rivals to drug gangs and to suppress indigenous and land-worker activism, according to the report.
Although Mr. Alston praised Pernambuco's new governor's efforts to rid the region's death squads, he concluded that the hundreds of people arrested so far only "represent the tip of the iceberg."
The most significant of the many factors leading to police participation in organized crime and in unlawful killings is the low conviction rate even in regular murder cases. In São Paulo, only about 10% of homicides are tried in the courts and only half of those result in convictions, according to the report.
"Clearly, the institutions for holding police accountable are broke, but they are not beyond repair," said Mr. Alston.
"My hope is that the detailed recommendations in my report will provide a starting point for undertaking the necessary reforms."