A simple solution to solving more crimes: Let people sleep

During criminal investigations, the victims, witnesses, and suspects interrogated are commonly exhausted: Perhaps they’ve been in custody overnight, or were awoken by a crime at 1 a.m., or have spent days in a hospital. This tiredness, it turns out, severely hampers investigators’ efforts.

Researchers at Iowa State University studied how sleep affects interrogation behavior. They did this by, well, interrogating 143 people about their own criminal histories. (Spoiler alert: The most common transgressions were underage drinking, illegal drugs, and DUI.) The sleep-restricted interviewees provided 7% less information to interviewers, like who, what, when, where, and why. Though 7% may seem insignificant, when magnified across five or 10 or 20 interviews in an investigation, it means investigators do not hear essential details. “Across 10 people they’re missing five pieces of critical information that they could use to corroborate or cross-check with other information,” says the study’s coauthor Zlatan Krizan, a professor of psychology at Iowa State University.

Counterintuitively, sleep debt detracts from people’s interest in spilling the beans. “People who had less sleep were not as motivated to recall information or found doing so required more effort to recall information,” added Christian Meissner, a professor of psychology at Iowa State University. Taken together, these findings suggest that investigators are shooting themselves in the foot when they wake up a suspect to conduct an interview.

The findings were published in Sleep.