AMES, Iowa - It's late at night inside a cramped interrogation room.
The suspect being questioned may have come straight from working a double shift or maybe they've been sitting at the police station for hours. Exhausted, it's hard to think clearly, and they just want this conversation to end.
Quick look
While research shows sleep-related fatigue affects how we think and feel, the impact of sleep loss on the reliability of statements and confessions in the legal system has received far less attention. A new research synthesis from Iowa State researchers examines this issue, including the need for evidence‑based standards to help judges and investigators recognize and account for sleep disruption in the legal process.
Scenarios like this aren't uncommon in the criminal justice system, said Zlatan Krizan, professor of psychology at Iowa State University.
"Many people who interact with the justice system - from suspects to witnesses - are exhausted, anxious and significantly sleep-deprived," Krizan said. "These factors can affect the statements people give."
Yet, Krizan added, the justice system has largely overlooked the impact sleep loss has on what people say during questioning.
"We know from years of research that sleep-related fatigue impacts our ability to think clearly, use judgment and recall events accurately," Krizan said. "But the role sleep loss plays in the evidentiary value of statements and confessions in the legal system has been far less explored."
In a new research synthesis published in Psychology, Public Policy, and Law, a journal of the American Psychological Association, Krizan and his two co-authors - Breanna Curran, a fourth-year doctoral student in social psychology at Iowa State, and Richard Leo, professor of law and psychology at the University of San Francisco School of Law- set out to explore this knowledge gap and better understand what happens when fatigued people enter the legal process.
Sleeping on a problem
Legal psychology has made progress in understanding what shapes the reliability of eyewitness accounts, victim statements and confessions over the years, Krizan said, but "most of that work has focused on stable factors like intellectual disabilities and mental health conditions, or temporary influences such as momentary stress or alcohol and drug intoxication."
"Awareness is growing that sleep deprivation can distort what people say in legal proceedings, but research on fatigue's impact still lags behind," Krizan said.
And because sleep is essential for brain health and behavioral functioning, disruptions to when or how long we sleep can impair attention, emotion and social behavior.
From a population perspective, Krizan said large-scale studies have found that people who interact with the criminal justice system tend to experience poorer, more disrupted sleep than the general population. He also noted this is especially true for people who have frequent police contact or for those who have experienced violence or trauma.
"Because many police interviews also take place at night, people often give statements while tired or at a natural low point in alertness," Krizan said. "This makes sleep‑related impairment especially likely during law-enforcement interactions."
Currently, U.S. courts judge whether a confession can be deemed admissible by applying two rules: the Miranda requirement that any waiver of rights must be knowing, intelligent and voluntary, and the Fourteenth Amendment voluntariness test, which excludes confessions obtained through coercive tactics that overpower a suspect's free will.
Krizan noted courts rarely suppress confessions simply because a suspect was sleep‑deprived, even though fatigue can seriously impair a person's ability to understand or voluntarily waive their rights. Aside from a 1944 Supreme Court ruling that deemed 36 hours of nonstop interrogation as inherently coercive, Krizan said there are no firm legal standards for how much sleep loss renders a confession involuntary if the interrogations occur in bouts.
Stages of distortion
Krizan and his co‑authors found that sleep‑related fatigue can distort statements at various points: 1) before reporting what happened, as fatigue can weaken the memory; 2) during initial contact with police, when tiredness can affect how engaged, clear or cooperative a person is; and 3) during questioning while in custody, as fatigue can make someone more vulnerable to pressure and more likely to give a false confession.
"Sleep loss can weaken eyewitness recall, reduce autobiographical detail, and increase susceptibility to misinformation and leading questions," Krizan said. "As a result, sleep‑deprived individuals are more prone to memory errors even in non‑confrontational interviews."
Krizan also emphasized that sleep loss can make stressful situations - like an interrogation - feel even more overwhelming. Its effects build over time, so long or high‑pressure questioning can hit especially hard.
"When someone is exhausted, they're more likely to focus on getting out of the stressful moment rather than thinking about long‑term consequences, which can push them toward complying just to make the situation stop," Krizan said. "Extreme fatigue can also create confusion and make people doubt their own memory, leaving them more open to suggestive tactics and even internalizing false information.
"Overall, sleep loss can lead people to make decisions that create relief in the moment but are far worse for them later - and especially problematic if they're innocent."
To really understand how sleep‑related fatigue shapes these outcomes, Krizan said researchers still need to dig deeper into how tiredness affects decision‑making, stress and confidence in one's own memories.
Bridging the gap: A preliminary framework
Krizan said law enforcement and courts need evidence‑based standards for recognizing and accounting for sleep disruption.
"We are proposing three simple, science-based benchmarks to help judges and investigators evaluate the impact of sleep disruption," he said.
The benchmarks are:
- Low-to-moderate impairment level - 24 hours without sleep or only four hours of sleep per night over two days. "This level of sleep-related fatigue exceeds the legal limit for blood alcohol concentration in most states," Krizan said, "and it places suspects at a higher risk of false confessions when faced with guilt-presumptive, accusatorial tactics."
- High impairment level - 48 hours without sleep or only four hours of sleep per night over four days. "At this level of sleep deprivation, the vast majority of adults will experience significant impairment in cognitive and emotional functioning compared to when they are well-rested," Krizan said. "And most importantly, this level clearly exceeds the 36-hour threshold of continued wakefulness that has been recognized by the U.S. Supreme Court as 'inherently coercive' when it occurs due to non-stop questioning."
- Extreme impairment level - 72 hours without sleep or only four hours of sleep per night over the course of one week. "This level of sleep loss would result in the onset of psychosis and extreme disruption of physiological functions," Krizan said.
Krizan and his team said sleep disruption needs to be documented, managed and weighed in legal decisions.
"Investigators should note when interviews occur, how long they last, along any signs of significant fatigue," Krizan said. "Sleep‑deprived witnesses and suspects are more prone to errors, much like those who are intoxicated or cognitively impaired. Simple protocols and routine video recording can help capture this information."
Krizan also noted overnight or extended interrogations increase vulnerability to coercion and false confessions because they are especially likely to disrupt sleep and induce fatigue. He said there is a simple message at the core of this research review.
"If we care about truth, fairness and due process, we cannot afford to treat sleep disruption as an afterthought," he said. "The legal system needs better documentation, better awareness and better standards, and the research community needs to help fill the gaps.
"Sleep loss isn't a minor variable; it shapes the reliability of the evidence on which justice depends."
