The study documents how an interrogator’s sleep and fatigue can affect interrogation success


Like many first responders, law enforcement and detectives often struggle with sleep. Late-night shifts, stress, and the 24-hour nature of crime can throw off biological clocks and shorten sleep cycles. Besides the negative health effects, new research indicates that stressed officers have a hard time gathering information that could bring justice for victims.

The study was led by Zlatan Krishan, a sleep scientist and professor of psychology at Iowa State University. He says previous research, including his own, shows that people who lose sleep have trouble controlling their emotions and keeping themselves on task.

Unfortunately, there hasn’t been a lot of research on the role of sleep for people with high-risk investigations. We wanted to see what real investigators and law enforcement officers experience during their investigative interviews because we know that they often sleep less than the recommended amount and suffer frequently from sleep disturbances.”

Zlatan Krishan, a sleep scientist and professor of psychology at Iowa State University

With ISU psychology professor Christian Messner, graduate student Anthony Miller, and retired homicide detective Matthew Jones, Krishan conducted a study with 50 law enforcement officers from Arizona, Iowa, Kansas, and Nevada. Participants wore an activity tracker while sleeping for two weeks and completed a daily survey that included questions regarding sleep quality, stress, work hours, and self-care (for example, hobbies and exercise).

Officers also report their interactions with victims, witnesses or suspects during actual investigation interviews in the field, which Krishan asserts is psychologically complex. In order to obtain useful information that can solve a case, he says, investigators need to establish a relationship or relationship with the other person. This can be difficult to do over a short interaction, especially if the interviewee is suspicious of law enforcement, trying to cover up a crime, or simply annoyed that their day has been interrupted. Investigators may need to change tactics or strategies.

“Conducting an effective interview requires significant cognitive effort and the ability to manage one’s emotions. Interviewers often informally report significant stress and sleep disturbance as part of the job. For the first time, the current study documents how sleep and fatigue of the interviewer can significantly affect interview success or interrogation,” says Messner.

Main findings

After analyzing data from sleep activity trackers and using bio-mathematical modeling to estimate daily fatigue, the researchers found that officers often:

  • I slept less than seven hours a night,
  • took longer than average to fall asleep,
  • I woke up several times during the night, and
  • I underwent several days with suboptimal levels of alertness, some of which were on par with mild levels of alcohol intoxication.

They also found strong evidence linking sleep to several key aspects of the investigators’ interviews. One of the more surprising findings was that the officers reported greater resistance than the interviewees and greater difficulty in establishing a relationship on the days when they were most stressed. One possible explanation, Krishan says, is that tired investigators are more willing to lose patience and see interviewees as uncooperative.

Another important finding from the study supported this. The sleep-deprived participants reported difficulties focusing on their work and managing their emotions. These results were most likely among officers working late-night and early-morning shifts.

“The results of the study indicated that less stressed officers and investigators may be better equipped to access investigative solutions and bring appropriate offenders to justice,” says Krichen. “Management of fatigue and the willingness to rest law enforcement are really important to ensure their effectiveness and to ensure valid results of investigations.”

Researchers point out that some professionals (for example, airline pilots) have rest requirements. But Krishan adds that sweeping enforcement of regulations like this would be difficult to enforce with police departments, which are run locally. They don’t have a national regulator like the Federal Aviation Administration or the American Medical Association.

He adds that these cases are not limited to law enforcement agencies. Other first responders, including firefighters and EMTs, often have sleep disturbances, work long shifts and are overworked, and are similarly managed at the city or county level. A solution could be to add more staff to relieve first responders, Križan says, but that comes with additional hurdles, including agreeing to larger budgets and finding qualified candidates.

While easy policy solutions remain a long way off, Krishan and his team continue to research how lack of sleep affects police officers’ ability to assess the credibility of interviewees. They are also studying how individual characteristics may make a person more or less sensitive to the negative effects of fatigue.


Journal reference:

Krizan, Z.; , et al. (2023). Effect of alertness versus fatigue on investigators in an actigraphy field investigation study. Scientific reports.


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