"These are not `isolated incidents` but a `pattern of behavior,`" warns the "Broken Blue Line" report, released Wednesday by the Johannesburg-based Institute for Race Relations.
"Violent crime levels in South Africa won`t turn around while the `wolf guards the sheep.`"
The study of 100 randomly selected media reports about alleged police crime was funded by Afriforum, an Afrikaner rights organization. Relatively petty offenses, such as bribe taking, were not considered.
Of the 100 incidents described, 32 were murders and attempted murders, 22 were armed robberies, and 26 were rapes, in addition to other serious offenses. The results were then compared against two additional sources of information on disciplinary action against police officers implicated in crimes.
According to the IRR, more than 1,400 serving police officers, or about one in 100, have a criminal record for serious, violent offenses.
While South African Police Service management is trying to deal with the problem of criminality on the force, there appears to be limited success. A 2011 version of the "Broken Blue Line" report found similar results, including a major problem with sexual violence by police.
The latest report describes "significant evidence of a trend" of police officers detaining women in order to rape them. South Africa has one of the highest recorded rates of rape in the world.
In a number of incidents reported by media, a police officer would stop a young woman in a public place, before taking her away to be raped in the back of a police vehicle and then setting her free.
"It is often with good reason that the public fear the police, especially with regard to sexual violence and rape perpetrated by officers against vulnerable women — the most frightening finding of the report," the report said.
South African police have faced numerous allegations of corruption and brutality in recent years.
A two-year audit of the country`s police service, released in 2013, found that of 157,500 officers, 1,448 of them had been convicted of crimes.
Responding to the report, the South African Police Service criticized the methodology as containing "dangerous generalizations, apparently mostly based on media reports, interviews with journalists and some form of engagement with the IPID [Independent Police Investigative Directorate, an independent oversight body]."
"We do not support it and feel that it was funded and released with malicious intent," Riah Phiyega, South Africa`s national police commissioner, said in a statement.