Why do innocent people confess?

When an innocent person confesses to a crime he or she didn't commit, there's a general assumption of inappropriate pressure in the interrogation process.

But Brandon Garrett, whose new book profiles the first 250 prisoners whose convictions were later overturned with DNA evidence, found that innocent people do in fact confess to crimes they didn't commit--even if they are not mistreated during questioning.

Garrett writes in Slate that in 40 of the 250 cases he studied, innocent people elaborately admitted to their alleged crimes, often using very specific details in their confessions. Since only 23 of those 40 interrogations were recorded--and those only partially--it's impossible to know whether police fed suspects details they worked into their stories, a forbidden practice. What Garrett did find, however, is that false confessions tend to come from the most vulnerable suspects:

Of those 40 exonerees who confessed, for instance, 14 were mentally disabled or borderline mentally disabled, and three more (at least) were mentally ill. Thirteen of the 40 were juveniles. All but four were interrogated for more than three hours at a sitting. Seven described their involvement in the crime as coming to them in a "dream" or "vision." Seven were told they had failed polygraph tests. Like Sterling, all of them waived their Miranda rights. Despite all these hints that their confessions were lengthy and coercive, and despite the fact that they were mostly vulnerable individuals, none had any luck challenging their confessions before trial. The confessions were thought to be such powerful evidence of guilt that eight were convicted despite DNA tests at trial that in fact excluded them as the culprit.

Mandatory recording of interrogations would bring greater scrutiny to the techniques used by police during interrogations that lead to confessions, Garrett writes.

(Screenshot from the false confession of Frank Sterling, a man who spent nearly 19 years in prison for murder before DNA evidence exonerated him.)