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Force Science explains “slips-and-capture errors”

And other psychological phenomena that drove the fateful BART shooting

Two expert witnesses with Force Science backgrounds are believed to have been influential in a jury’s recent decision to reject a murder conviction of a former transit officer accused of deliberately shooting an unarmed suspect in the back during a handcuffing scuffle.

The witnesses, Dr. Bill Lewinski, executive director of the Force Science Institute, and retired LAPD captain Greg Meyer, a certified Force Science Analyst, testified in detail how a combination of inadequate training and psychological stress phenomena most likely led to a tragic accident in which the officer mistakenly drew his sidearm instead of his X26 Taser while trying to restrain the struggling suspect. The prosecution had claimed the incident was one of intentional homicide by an out-of-control cop.

“This case,” Lewinski told Force Science News, “is a classic illustration of powerful forces beyond an officer’s conscious awareness that can shape a threatening encounter. These forces may not be readily evident even to unbiased witnesses, but in a matter of seconds they can change the lives of those involved forever.”

From the witness stand, Lewinski and Meyer explained how, in their opinions, psychological concepts such as “slips-and-capture errors” and “inattentional blindness,” along with equipment positioning and an absence of stress-inoculation training, became driving factors in the controversial case.

Although the officer was exonerated of murder, he was convicted of a lesser charge of involuntary manslaughter. At this writing, he has not yet been sentenced.

Recapping the incident

Accusations against the defendant, 28-year-old Johannes Mehserle, have been exhaustively covered by many mainstream media. Briefly recapping: In the first minutes of 2009, Mehserle and fellow officers with northern California’s Bay Area Rapid Transit system were on a station platform in Oakland, trying to control several rowdy New Year’s Eve celebrants who’d been fighting on a BART train.

In the presence of a hostile crowd, Mehserle and Ofcr. Anthony Pirone were attempting to control one suspect, Oscar Grant III, age 22. According to one trial participant, Grant had “a long and colorful criminal history,” including at least one arrest in which he tossed aside a gun during a foot pursuit, although the BART officers had no knowledge of this at the time.

Pirone had Grant’s head and shoulders pinned down with his knee, while Mesherle was trying to tug Grant’s right hand out from under his body for cuffing. Grant was actively resisting.

At what turned out to be a critical juncture, Mehserle twice announced, “I’m going to Tase him!” He then drew his Sig Sauer semiauto with his right hand—not his Taser, which was on the left front of his body in a cross-draw position—partially stood, and fired a single, fatal shot into Grant’s back. The action was captured on video by a multitude of civilian cell phones.

Mehserle soon resigned from the department. He never spoke to the press, but privately he insisted from the beginning that the shooting was a horrible mistake; he thought he was firing his Taser when he fired his gun. But Mehserle is white, Grant was black. Outraged relatives and activists immediately branded the shooting a willful act of murder, motivated by racism—a theme the prosecution sought to promote when Mehserle finally was brought to trial for murder recently. (A change of venue had shifted the matter to a courtroom in Los Angeles.)

Mehserle’s attorney, Michael Rains, called Lewinski, an internationally recognized authority on human behavior in force confrontations, to explain to the jury of four men and eight women how the shooting could possibly have been an accident when the officer’s actions looked so cut-and-dried incriminating in the videos.

Analysis on “slips-and-capture errors”

In an interview with Force Science News, Lewinski reconstructed the analysis he laid out for the jury.

What was involved in this shooting, he says, is a well-researched, well-documented psychological phenomenon called “slips-and-capture errors.”

“These are mistakes that are made when you think you are doing one thing but you actually are doing another and the result often is directly opposite of what you intended,” Lewinski says. “In effect, your intended behavior ‘slips off’ the path you wanted it to go because it is ‘captured’ by a stronger response and sent in a different direction.

“In Mehserle’s case, a variety of compelling elements—including urgency, time compression, narrowed focus of attention, and automatic response—conspired to create a fateful slip-and-capture.”

As we’ll see in more detail in a moment, Mehserle had had scant experience with drawing or using a Taser, none of it in stressful circumstances. He’d carried a Taser while working only about 10 times and had drawn it in training half a dozen times, on duty perhaps three.

By contrast, he’d been drawing his sidearm an estimated 50 times a week as practice since graduating from the academy about two years earlier. “He’d practiced drawing very fast and had built a strong automatic motor program,” Lewinski says. “Upon recognition of a threat, you want to be able to draw without having to consciously think about each mechanical step in the process so you can focus on the threat and the decision-making involved in resolving it.”

Dealing with the stubbornly resistant Oscar Grant amidst the angry crowd was a high-stress event that suddenly escalated to an even more intense level. In Grant’s wiggling his hand around under his body and refusing to yield to Mehserle’s yanking on his arm, Mehserle perceived that the suspect was trying to reach first into his waistband and then into his right-hand pocket.

“Earlier that evening, Mehserle had witnessed the arrest of another suspect who turned out to have a gun in his right front pocket, and on three other occasions he and his partner had made other arrests where that was the case,” Lewinski says. “In that context, he interpreted Grant’s uncontrolled hand movement as potentially life-threatening and, with his emotional intensity now ratcheted up, announced the decision to Tase him.”

Analysis on Taser intention

Mehserle, testifying in his own defense at the trial, said he thought at that moment, This has to go quick.

“All his actions from that point forward—except one—are consistent with a Tasing intention,” Lewinski says. “Enhanced video frames show his hand canting and tugging at his holster at an angle that suggests a Taser-draw effort. He persists in this effort to the point that he defeats the restraints on his gun holster. His thumb then moves as if to arm the Taser, he backs up to create a better dart-spread, he only fires once instead of double-tapping, and so on.

“The only inconsistency—and, of course, a critical one—is that he reached to the right side of his belt and gripped his gun instead of crossing his hand about a foot away to the left where his Taser was.

“This is the slip and capture. Under time pressure to address a perceived threat, his intention to draw his Taser slipped off his agenda, so to speak, when it was captured and completed by a more well-rehearsed motor program; i.e., going to the location where his gun was in order to manage a threat. He was not conscious of this unfortunate switch until after the shot was fired.”

Such errors are common in civilian life, Lewinski explains, ranging from experienced pilots who inadvertently activate the wrong controls at a critical moment and crash airplanes to drivers who floorboard their accelerator when they think they’re tromping on the brake. “In a very simple illustration,” Lewinski says, “think of renting an unfamiliar model of car. You know you’re in a different vehicle, but when you go to insert the key you may automatically and unconsciously direct it toward the spot where the ignition is located on your own car at home.

“The fact that you do this once is not unusual, but the fact that some continue to do it several times before their behavior changes shows how powerful old programs are and how hard they are to change.

“In a situation like that, you get the benefit of an attentional check—you see what you’ve done wrong and then you pay attention and correct it. But there wasn’t time for that for Mehserle.

“In his urgency, his concentration was focused exclusively on Grant’s back, where he intended to place the Taser darts. Because of what’s called ‘inattentional blindness’—meaning that he wasn’t consciously paying attention to and registering it—he wouldn’t have been aware that the feel and weight of the gun was different from that of a Taser. The video clearly shows that the gun was never brought up to his line of sight, where he might have seen that it wasn’t his yellow Taser.

“His first indication that he’d made a mistake was when he pressed the trigger and the bullet tore into Oscar Grant’s back. The video shows him experiencing a definite reflexive, startle reaction. His left hand comes away from the gun as if he’s touched a hot stove. His hands go to his head and he exclaims, ‘Oh my God!’ His response is consistent with a sudden realization that he’d done something drastically wrong.”

In his testimony, Lewinski cited the research of Drs. Alexis Artwohl and Audrey Honig, both experts on police psychology and graduates of the certification course in Force Science Analysis. In their studies, Artwohl and Honig have documented that the vast majority of officers default to automatic, unconscious defensive behavior in threat situations, similar to some of what Mehserle experienced.

Crucial shortcomings in training

On cross-examination, the prosecution team did not attempt to rebut the concepts Lewinski had described. Nor did they offer significant challenges to the testimony of Greg Meyer, who pinpointed the shortcomings in training and equipment provided by Mehserle’s agency at the time of the shooting.

Improvements have been made since then, but before the shooting BART did not issue Tasers and holsters consistently and permanently to individual officers, related Meyer, a well-known less-lethal force expert who formerly headed LAPD’s training academy. On a given shift, an officer could end up with any of four different holster configurations and belt placements. (This, in Lewinski’s opinion, contributed to the risk of slips-and-capture errors.)

Moreover, Meyer testified, BART did not put officers through any dynamic, stress-inducing scenarios requiring force-options selection as part of their training for Taser use. He considers that essential for “truly testing an officer’s ability to be ready for stressful encounters on the street.” Lewinski fully concurs.

Meyer presented an exhibit for the jury documenting six other known “weapons-confusion” cases in recent years in which an officer shot someone while intending to use his or her Taser. None of those officers was criminally prosecuted. However, all, like Mehserle, had Taser placements that required a dominant-hand draw, and all the incidents occurred under high-stress conditions.

Meyer was not permitted to mention in court that after Mehserle’s shooting, BART changed its policy to require Taser placement and holster design that accommodates only a “weak-side, weak-hand” draw, which both Meyer and Lewinski consider the safest configuration. (“Even then, because of the powerful psychological factors often involved, there may still be weapons-confusion errors that result in unintentional shootings,” Lewinski cautions. “But this placement and design is highly likely to reduce the risk.”)

Defense against racial accusations

During his appearance on the witness stand, Meyer managed to deliver a deft blow to the prosecution’s attempt to frame the Mehserle shooting as a racial incident. This turn of events was not reported in any mass media coverage of the trial, Meyer told Force Science News.

On video of the confrontation on the platform, Ofcr. Pirone can be heard using an inflammatory phrase containing a racial epithet in a verbal exchange with Oscar Grant. Anticipating this as an issue that would arise at trial, Meyer took the tape to a highly skilled sound technician at a Hollywood movie post-production facility who was able to clarify and amplify the sound track so that both sides of the exchange could be heard.

In court, Meyer was able to present what the technician’s work had revealed: It was actually Grant who had first used the derogatory phrase, as part of a profane diatribe directed at Pirone. Pirone unfortunately twice repeated the phrase back at Grant in a questioning manner, providing fodder for the prosecution to try to portray all officers at the scene in a bad light.

Lewinski, too, offered a surprise to the prosecution in court. On cross-examination, a prosecuting attorney attempted to establish that Lewinski could not be impartial in any case involving a law enforcement officer. Lewinski countered by pointing out that two investigators from the agency investigating the shooting had contacted him soon after the incident and he volunteered to explain to them the Force Science interpretation of what had happened. The investigators, however, never called back to follow up.

The jury’s decision

In his instructions to the jury, Superior Court Judge Robert Perry advised the panel that it could acquit Mehserle of any criminal wrongdoing or could find him guilty of second-degree murder, voluntary manslaughter, or involuntary manslaughter. The jury found the latter, concluding that Mehserle had not intended to kill Grant but had “acted recklessly” in the confrontation.

Defense Atty. Rains said he felt that the Force Science testimony was “extremely well” received by the judge and jury and he was confident it was “very important” in the jurors’ decision to rule out conviction on the most serious charges.

Still, he and the witnesses as well feel Mehserle should have been fully acquitted under the circumstances. The officer “made a fateful mistake that caused a death,” a reporter quoted Rains as saying, but the mistake “was not criminally negligent.” He says he will argue that position at what is expected to be an extensive sentencing hearing scheduled for November.

Meanwhile, Mehserle sits in jail, facing possible prison time from this verdict, as well as a federal investigation of whether he violated Oscar Grant’s civil rights and a pending $25 million civil suit filed against BART by one of the plaintiff’s attorneys in the Rodney King case. BART has already paid $1.5 million to Grant’s 5-year-old daughter.

Psychological factors involved in the Mehserle case, including slips-and-capture errors, will be explored in greater detail in future Force Science Analysis certification courses. For more information on course content and registration, e-mail

The FSRC was launched in 2004 by Executive Director Bill Lewinski, PhD. -- a specialist in police psychology -- to conduct unique lethal-force experiments. The non-profit FSRC, based at Minnesota State University-Mankato, uses sophisticated time-and-motion measurements to document-for the first time-critical hidden truths about the physical and mental dynamics of life-threatening events, particularly officer-involved shootings. Its startling findings profoundly impact on officer training and safety and on the public’s naive perceptions.