There have been increasing calls for police to wear body cameras following a spate of cases, especially in the United States, of police violence and killings of unarmed people caught on camera.
"It seems from some of the early studies that ... up to 60 per cent of the use of force (is) reduced when police wear body cameras," UN Special Rapporteur Christof Heyns told a briefing.
He said complaints of the use of excessive force had meanwhile declined by 90 per cent, according to the studies.
There was as well a marked decrease in what he called the "trigger happy" approach. Heyns, who in 2011 spearheaded moves to authenticate a five-minute video clip showing atrocities in Sri Lanka during the government's war against Tamil separatists, however said that new technology had led to a "digital divide" with unfilmed violations risking being ignored.
"A mindset may arise that unless a body camera was used, the police or the courts or the human rights community should not look at it," he said, adding that human oral testimony risked being ignored "because it is not as vivid as what one may get from a body camera or from what is shown on television."
"There is the danger of the digital divide. The idea that if it not digital then it does not exist," he said. "The whole human rights system is geared towards using information and communications technologies but it may be ignoring violations in large parts of the world that are not as connected as other parts," he said.
Heyns also said the police could misuse body cameras. "If the police have this very wide right of wearing cameras when they enter people's homes and record," they might do it to "invade their privacy and have footage of people in a compromising position," he said.
"The cameras may be switched off at crucial moments," he said, to make something sinister "look like it was actually an innocent kind of interaction."
Body cameras are relatively expensive, costing an estimated USD 1,000 in the United States, where a series of brutal rights violations by police have prompted international outrage and growing domestic calls for more police to use them.
Although still a new innovation in the US, experts predict they could become standard equipment in the next three to five years.