North Carolina prosecutors have sought the death penalty against about two people per year since 1989 without enough evidence to prove their guilt, according to the Center for Death Penalty Litigation. The advocacy group opposes the death penalty and helped represent former death row inmate Henry McCollum, who was recently exonerated after 30 years in jail.

Executive director Gretchen Engel says stories like McCollum's trouble people who want to believe that false imprisonment is a problem of the past. The new report disproves that notion even for those who are never convicted, Engel says.

"It's been persistent, consistent. And it's the same kinds of problems that we see in exonerations: reliance on paid snitches, unreliable junk science, coerced confessions," she said. "All the things that we see in exonerations are what we see in these cases."

North Carolina spent nearly $2.4 million in defense costs to pursue failed capital cases over the last 25 years, according to the report. The North Carolina Conference of District Attorneys declined to comment, saying representatives have not had time to properly review the cases in the report.