WASHINGTON (AFP) - A record number of wrongful convictions were overturned in 2013 due in large part to tougher policing, but many more unjust decisions were left in place, according to a report released on Tuesday.
Out of almost 1,300 criminals whose convictions were overturned in the past 25 years, 87 were exonerated in 2013, the briskest pace since 2009, when 83 were cleared, the National Registry of Exonerations study said.
"2013 was a record-breaking year for exonerations in the United States... The difference is bound to grow as we learn about additional exonerations that occurred in 2013," the report said.
"That's good news because we are more likely to address the problem that caused false conviction in the first place," the report's lead author Samuel Gross told AFP.
"But these cases that we know about so far are only a small proportion of errors that actually occur. Most times, they're never discovered." Contrary to popular belief, DNA evidence only plays a role in 20 per cent of exonerations, the registry found.
In 38 per cent of cases, convicts were exonerated "at the initiative or with the cooperation of law enforcement," the report found.
"More people are now paying attention to wrongful convictions. Police, prosecutors, judges, defense attorneys and the public are all more aware of the danger of convicting innocent defendants," Mr Gross said.
"A lot of the credit goes to prosecutors and police who are increasingly active in investigating possible false convictions. But there are many false convictions that we don't know about," he added.
"The exonerations we know about are only the tip of the iceberg." Fifteen of the 87 exonerations in 2013 - 17 per cent - concerned defendants who were convicted after pleading guilty, also a record.
Innocent people sometimes "plead guilty because they were afraid that if they went to trial they'd be convicted and would get a prison sentence that is much longer than with a guilty plea," Mr Gross explained.
"Perhaps they'd even be sentenced to death," he added. "They plead guilty to avoid that danger."
Mr Reginald Griffin, who was sitting on Missouri's death row, had his conviction overturned in 2013, after 25 years behind bars. That brought to 143 the number of death row inmates exonerated nationwide.
The study found more than half of all exonerations - 56 per cent - were attributed to false accusations or perjury from witnesses.
Another 46 per cent were attributed to official misconduct, while just over a third, 38 per cent, were due to mistaken eyewitness identification. Some exonerations were linked to more than one cause.