ISU researchers measure fatigue in suspect confessions, statements to police

by Brooklyn Draisey, Iowa Capital Dispatch
March 27, 2026

Iowa State University researchers are hoping to establish a foundation for further consideration of sleep and the lack of it when it comes to justice system proceedings, from suspect interrogations and confessions to, eventually, jury considerations.

Zlatan Krizan, a professor of psychology at ISU, and social psychology doctoral student Breanna Curran, co-authored a research synthesis into how interrupted sleep and continued wakefulness fit into the legal system. They developed guidelines that could work as a starting point for those in the legal system to determine someone’s ability to give an accurate and voluntary statement to law enforcement.

The pair hopes their work will lead to further research and more buy-in from attorneys, judges and others involved in the justice system.

“You’re trying to enrich interpretations that attorneys and judges are doing, such that they’re really more tethered to reality or science or what do we now know, without trying to make the decision for them, as I say, because it’s really not our job in that sense,” Krizan said.

The team developed benchmarks for different levels of sleep disruption and how it might impact the validity of the evidence suspects or defendants provide. Their work used existing research from different areas of behavioral science — the science of memory, sleep and circadian science relating to human functions, and the study of interrogation methods, Krizan said — as well as analysis of court cases and precedents.

Krizan said listening to discussions among his colleagues, many of whom are experts in psychology and law, was what drew his interest as someone who studies sleep and fatigue and how they impact people’s ability to function.

In looking at the current literature on the topic of sleep deprivation and its impacts on legal proceedings, Krizan said that beyond a few papers and other works mentioning the topic, there wasn’t evidence of any systematic look into the subject.

“It really seemed like a great opportunity to fill in lots of blanks that have been suggested by various scholars and legal scholars and people who worked in this area, but haven’t really kind of taken it on,” Krizan said.

The theoretical analysis developed by Krizan and Curran, as well as University of San Francisco law and psychology professor and report co-author Richard Leo, is a ”culmination” of the more of five years of thinking into this topic, Krizan said, alongside the conversation he and Curran have had throughout her years on campus.

The three benchmarks proposed in the team’s report map impairment levels from low-to-moderate to high to extreme, based on how many hours without sleep someone has racked up or how many days they’ve had only four hours of sleep.

Krizan said the different levels of impairment can bring with them losses in cognitive and emotional functions, such as altered memory and becoming increasingly overwhelmed in stressful situations.

When it comes to impairments to those going through the legal system, Krizan said U.S. courts have generally maintained that the state is not responsible for any impairments it did not cause, with “one bright line in constitutional law” that defines 36 hours of continuous questioning as coercive.

“A big chunk” of cases where things have gone wrong, identified by the DNA Exonerations Database maintained at Duke University, included false confessions, Krizan said, as well as often “coercive interrogation strategies” that lasted six hours or more. With many interviews starting in the evening and going throughout the night, Krizan said sleep disruption was “part of the vulnerability picture” for certain cases.

In reviewing these cases, Krizan said there wasn’t much discernment as to how much someone had slept, if any at all, and investigators need to be tracking fatigue and keeping its dangers in mind.

Beyond the benchmarks, Curran said there are gaps in guidelines for dealing with impairments that impact the “overall vulnerability and suggestibility of a person.”

“I think it’s something throughout the entire investigation process, both on the side of victims or suspects, but also on the other side, because sleep comes into play too with law enforcement and how they do their job,” Curran said. “And I think overall, sleep comes into play in multiple different areas.”

Getting these guidelines applied “in the real world” is the end goal of the team’s work, Curran said, but their very existence highlights gaps in research and provides a basis for other researchers to go further in this area of study.

Preliminary data has already started coming in on a study the pair is pursuing into how juries perceive impairments like lack of sleep, Krizan said, which seems to show that while jurors do recognize it as impairing, it might not lead them to discount confessions.

Curran, now in her fourth year of doctoral work, said it has been it’s been an “insightful” and “cool opportunity” to go through this process with Krizan, from conceptualizing ideas to working on related projects, diving deep into the research and creating a body of work that can help “initiate change” in the world.

“I think it just really speaks to how scientists or psychologists, or the psych and law field, can make a difference in processes and cases and and things of that nature,” Curran said.

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