First, there was the unfamiliar skyline on the fourth floor of the parking garage. Typically, Amber Guyger parked on the third. Then, there was the bright red mat conspicuously marking the foreign door. And, finally, the stench of marijuana emanating from the apartment that Guyger claimed she mistook for her own before shooting dead its occupant, Botham Jean.
How could she miss so many obvious signs?
Because she was exhausted, her defense team has claimed. She’d just gotten off a 13 1/2 hour shift and was functioning on “autopilot.” To support their claim, the defense will call to the stand Charles Czeisler, a preeminent sleep deprivation scholar at Harvard University.
The Observer asked one of Czeisler’s collaborators, David Dinges, to explain what to expect. Dinges is a professor of psychiatry and chief of the Division of Sleep and Chronobiology at the University of Pennsylvania. He also served as an expert witness in the aftermath of the Exxon Valdez oil spill, a disaster later attributed to errors made by a fatigued sailor.
“I think there'll be a lot said in the direct and cross examination of the expert regarding what was the sleep schedule of the person. How much had they been on night shift, day shift?” said Dinges said.
Chronic fatigue can cause people to make mistakes, Dinges said. “And the mistakes can be simple ones, even on tasks that you do routinely,” he said.
Mistakes resulting from fatigue usually involve forgetfulness or mistaking one thing for another. But they can also involve actions, Dinges explained, where “somebody does something suddenly that they shouldn’t have done.”
But the key word here is chronic. If Guyger had had a good night’s sleep prior to her shift, “then you wouldn't really expect anything terribly dramatic,” Dinges said, particularly because it was a day shift when she would, presumably, normally be awake.
But problems can arise, he said, if the deprivation is routine. Shift workers who work odd hours with inconsistent schedules are particularly at risk, he said, particularly if they are given few days to catch up.
“Working shifts day in and day out, extra shifts, then you can expect a cumulative deficit,” Dinges said.
A 2003 study by Dinges found that people who slept four hours a night for a week had three times the number of mistakes in a simple alertness test as those who got a full eight hours.
On Tuesday, the prosecution walked through Guyger's work schedule. In the two weeks prior to the day of the shooting, her timecards indicated that she had worked nine regular shifts and 13 hours of overtime.
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It is still unclear how much she was working off duty. The Dallas Police Department has come under criticism in the past for allowing its officers to work excessive hours. A report released last year found that officers were allowed to work 72 hours at off-duty jobs, a practice that “does not consistently align with best practices,” city auditors wrote.
It’s not an isolated issue. National surveys have found that police officers get some of the least sleep of all professions, and a 2013 study of nearly 500 cops by researchers at the Centers for Disease Control and Prevention found that 40% reported feeling drained. This correlated with on-duty injuries, the study reported.
Officer fatigue can lead to other consequences as well. In a 2011 study co-authored by Czeisler, researchers found that sleep-deprived cops had a significantly higher rate of serious administrative errors and outbursts of uncontrolled anger, according to self-reported surveys.
Dinges hinted at the difficulty the jury may face in the coming days. Because of the range of factors that can determine fatigue's impact on someone's mental state, "It's hard to get a really simple answer," he said.