The number of exonerations in the United States of those wrongly convicted of a crime increased to a record 87 during 2013, and of that number, nearly one in five had initially pleaded guilty to charges filed against them, according to a report to be released on Tuesday as part of a project led by two university law schools.

Nearly half of the exonerations — 40 — were based on murder convictions, including that of a man wrongly convicted and subsequently sentenced to death in the fatal stabbing of a fellow inmate in a Missouri prison in 1983, according to the report by the National Registry of Exonerations. The registry is a joint program of the University of Michigan Law School and the Center on Wrongful Convictions at Northwestern University School of Law.

The previous record of known exonerations in the country came in 2009, when the group reported 83. The organization said it has documented 1,300 exonerations since 1989, most of them after convictions for murder, rape or other sexual assaults.

Fewer exonerations than in the past involved DNA evidence, a circumstance the registry attributed to the police and prosecutors exhibiting greater concern about the problem of false convictions.