Slow-motion video 'makes murder juries more likely to convict'

Slow-motion video replays shown to juries may be distorting the outcomes of trials, according to a new study.

US researchers found that viewing a killing only in slow motion made a jury three times more likely to convict of first-degree murder.

The study concluded that slowing down footage of aggressive offences caused viewers to perceive greater intent to harm than when viewed at normal speed.

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The use of video evidence has rocketed in recent years, with smartphone recordings, CCTV and footage from officers' on-body cameras all routinely accepted by courts.

Sometimes these recordings are shown to juries in slow motion, to help them decide what happened at often fast-moving and chaotic crime scenes.

However, in many murder trials, a crucial point of dispute is the intention of the accused. So the researchers showed participants, acting as jurors, a video recording of an attempted robbery of a shop, which ended with a worker being shot dead.

The "jurors" were shown either normal speed or a slowed down footage. Watching the slow-motion version quadrupled the odds that they would begin their deliberations ready to convict.

"Slow motion can be a better version of reality, sometimes it's very helpful for seeing how actions unfolded," said report author Eugene Caruso, of the University of Chicago.

"But at the same time we found that it seems to have an effect on our perceptions of someone's inner mental states and there it's really not so clear that slowing things down gives us a more accurate perception of what was going on in someone's mind at the time they were acting."