Explainer: The 'slip and capture' argument in ex-cop Kimberly Potter's case

Potter faces manslaughter charges after she fired her gun, killing Daunte Wright shortly after warning she was going to tase him

A sign reads 'kim potter trial. 9mm does not equal taser'
Signage honoring Daunte Wright and condemning former Brooklyn Center police officer Kimberly Potter lines the grass outside the Hennepin County Government Center in Minneapolis as jury selection in the trial of Potter began on Nov. 30.
Tim Evans for MPR News

If you’ve ever gotten in your car and started driving to work on your day off, you may have experienced what psychologists refer to as “slip and capture” or “action error.” These terms refer to when you automatically do something routine when you intend to do something else. 

They’re one of the key elements in the defense of former Brooklyn Center police officer Kimberly Potter for the shooting death of Daunte Wright. An expert witness is expected to testify that this can result in people making serious errors — such as reaching for a gun when they meant to grab a Taser. 

The defense is hoping this type of defense will convince jurors of how Potter, then a veteran police officer, could have made an apparently fatal mix-up when she shot and killed Daunte Wright in April during a traffic stop.

All people experience some degree of the phenomenon. But the stakes are a lot higher when it involves law enforcement, said Paul Taylor, a former police officer and assistant professor of criminal justice at the University of Colorado in Denver. 

“We do it all the time. Most of the time, again, those sort of errors are innocuous,” Taylor said. “In this circumstance, it’s catastrophic.”

Potter’s defense is arguing that she accidentally fired her sidearm when she meant to fire her Taser at Wright. The bullet went through his heart, and the car he was driving careened down the street and hit another vehicle head-on, injuring its two occupants and the passenger in Wright’s car. 

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A judge sp
Judge Regina Chu speaks during jury selection in the Kimberly Potter manslaughter trial on Dec. 1.
Screenshot of Court TV video

Prosecutors sought to exclude testimony from an expert witness the defense plans to call to testify about this sort of “action error” because they argued it wouldn’t help jurors understand the evidence. But Judge Regina Chu ruled that he could testify about the phenomenon, although he couldn’t testify that Potter actually experienced a “slip and capture error.” 

The expert, Dr. Laurence Miller, is a psychologist in Palm Beach County in Florida. He’s testified at previous trials involving police officers, including the trial of former Chicago police officer Jason Van Dyke for the shooting death of Laquan McDonald. Critics have argued that he’s wrong to apply psychological principles to incidents where police use lethal force because it’s based on shaky scientific ground

The “slip and capture” argument has been made before. Expert witnesses testified that it played a role in a 2009 incident in Oakland, Calif., where a transit officer shot and killed Oscar Grant, but later testified that they’d intended to use their stun gun. 

Prosecutors will be arguing that officers should be held to a higher standard because they’re entrusted with legal authority to use force in some cases, said Georgetown Law professor Angi Porter.

“They’re not trying to say that she premeditated, planned, to shoot Daunte Wright,” Porter said. “But they’re saying that this type of mistake is not tolerated in our society.”

Judge Chu ruled that it’s up to the jury during trial to establish the credibility of an expert witness who testifies about a concept like “slip and capture.” 

Porter said judges typically stay out of assessing whether an expert witness is credible, but prosecutors may try to discredit the expert before the jury. One thing prosecutors may focus on is the expert witness’s experience testifying in trials. Miller has testified largely for defendants. 

“If they’ve been an expert in 20 trials, and they’re all in defense of police, the jury gets to hear lines of questioning on that, and they get to doubt whether this is real science or whether this person is sort of routinely just out here to defend a certain type of profession,” Porter said. 

Applying the concept to police officers is controversial, said James Densley, a criminologist at Metropolitan State University. He said it’s just another way of saying “human error under stress.” But the fact that police officer mistakes can take someone’s life is the reason that officers are required to undergo extensive training and continuing education. 

“All humans make mistakes under stress — you don’t need terminology like this to emphasize that,” Densley said. “You could equally say that Kim Potter made a ‘brain fart,’ but that wouldn’t sound nearly so authoritative or convincing for the jury.”

Just because Potter may have made a mistake doesn’t mean she isn’t criminally liable, Taylor said. But he sees the larger issue being that Tasers and guns function too similarly. He wants to see Tasers designed to be fired in ways that don’t mimic a gun. He said even more training might not help if that change isn’t made. 

“It comes down to diminished attentional capacity during encounters that require attention to be devoted outward, and we’ve got a tool that functions in the exact same way as a firearm,” Taylor said. “I don’t think training is going to diminish that. In fact, if you spend a lot of time with both tools and you train them to the point of automaticity, you’re probably going to exacerbate the problem more than anything.” 

Potter’s trial continues throughout the week. The judge has said she hopes to wrap it up before Christmas Eve.