Can slow-motion video bias jury trials?

With the proliferation of police officers' body cameras and popularity of citizens live-streaming run-ins with the police, it's increasingly likely that court testimony isn't just one memory of how events unfolded held up against another. More and more, there's video evidence to consider as well. 

But researchers now warn that video evidence should be treated with caution in the courtroom, and the court of public opinion.

A study published in the Proceedings of the National Academy of Sciences found that viewers who watched a slow-motion video of a crime were more likely to say the crime was calculated rather than impulsive, even if they also saw a regular speed version of events unfolding as well. And premeditated crimes result in harsher sentences, according to study authors Eugene M. Caruso and Zachary C. Burns, business professors from the University of Chicago and the University of San Francisco, respectively. [Editor's note: An earlier version misspelled Dr. Caruso's name.]

Although a slow-motion video might help to make sense of a chaotic crime scene, it could also lead viewers to read intent into actions, "giv[ing] viewers the false impression that the actor had more time to premeditate before acting," researchers wrote. Judging whether a defendant had a long enough time window to consider inflicting harm is key in many legal disputes.

In the study, juries who saw the slow-motion video of a fatal shooting outside a convenience store were nearly four times more likely to return a unanimous first-degree murder verdict than juries who saw the regular-speed version, according to one of the four experiments.

This experiment was based closely off a real-world scenario. In a 2009 Pennsylvania trial, John Lewis pled guilty to the murder of a police officer who arrived on the scene of his armed robbery of a Dunkin' Donuts. Since the issue of guilt was certain, the question left up to the jury was whether he acted out of panic or with a “willful, deliberate and premeditated” intent to kill.

Two seconds elapsed from the time the cop appeared at the door to when Lewis fired the fatal shot – a two seconds the jury analyzed both in real time and slow-motion surveillance video. The jury decided that the murder was premeditated, opening the door for the death penalty, rather than reflexive, which could be punished with life in prison at most.

In appealing the first-degree murder charge, the defense argued that the fact that the slowed tape artificially stretched the time period during which Lewis made his decision to shoot created a "false impression of premeditation." The prosecution held that jurors were fully informed of how much time lapsed in reality, both by a timer superimposed on the slowed video and the fact they saw the regular speed version as well.

The Supreme Court of Pennsylvania denied the defense's appeal, and Lewis is currently on death row.

The authors of the slow-motion video study argue that their findings are strikingly consistent with John Lewis's defense team's claim. In one experiment, they showed participants both the regular-speed and slow-motion version of events, and while bias was reduced, it was not completely eliminated. Juries who saw both versions of events were still about 55 percent more likely to unanimously reach a first-degree murder verdict than juries who only saw the real-time version. 

"If jurors perceive video as a particularly 'objective' representation of true events, its biasing potential may be especially pernicious," the researchers write, though they don't suggest slow motion video should be thrown out of courts altogether. Instead, they say, the benefits, including a more complete understanding of contextual events, should be weighed against the costs, particularly a skewed impression of the perpetrator's mental state.