A record number of people exonerated for crimes they did not commit were put in prison because of official police, prosecutorial, or government official misconduct, according to new data.

Eighty-four of the 139 exonerations involved misconduct, the numbers released by the National Registry of Exonerations showed.

Overall, fewer wrongfully imprisoned people in the US were freed in 2017 than in years prior as well. The total number of people who have been falsely convicted is unknown, but last year 139 people were released, compared to 171 cases in 2016.

Other issues involved in the wrongful conviction these individuals were mistaken eyewitness testimonies, false confessions, false accusations, and perjury.

But, Ekow Yankah, a professor at the Cardozo Law School in New York, told The Independent that prosecutorial and police misconduct are the larger underlying issues.

For instance, the 2017 data showed that 96 people, in addition to the 139 individuals, were released through a “group exoneration” in Baltimore, Maryland and Chicago, Illinois after it was found that groups of police officers in both cities had been methodically framing them for drug crimes.

Combating it is something both groups like the Innocence Project - a group based in the Cardozo Law School which works mostly on DNA evidence-based cases to help free the wrongfully convicted - and prosecutors’ offices around the country are attempting.

It is a “long-term” problem Mr Yankah said, noting that there are political and litigation-related ways to make prosecutors “live up to their obligations”.

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Mr Yankah the key is also figuring out how willing prosecutors are to actually look back through their cases and admit to mistakes or actual misconduct, the setting of “conviction integrity” units that do more than just “resist” the work being done by groups like the Innocence Project, and taking into account how many of the convicted just “plea out, suck it up and serve their time” rather than going through what they perceive as a corrupt system.

Mr Yankah said that part of the underlying problem is prosecutors’ willingness to look back on their cases and set up “conviction integrity” units that will do more than just “resist” the work of outside groups that work to exonerate people who have been wrongly put in prison.

As NPR reported, “in all, 98 of the exonerations involved violent felonies: including homicides, child sex abuse convictions and sexual assaults of adults. In 66 of the cases, no crime was actually committed. Four of the homicide exonerees had been sentenced to death”.

There was also a steep decline in exonerated drug convictions - from 61 to 16 - between 2016 and 2017. The number can likely be explained by a backlog of cases being cleared in Houston, Texas where it was found that several defendants who had pleaded guilty were convicted for substances that were not actually illegal drugs.

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Ledura Watkins, 61, of Michigan spent an astonishing 40 years in prison for murder before being released and exonerated in June 2017.

The data also showed that Texas had the highest number of those exonerated last year with 23, followed by Illinois, Michigan, and New York.

Though the numbers released may appear small, it is the trend they represent that is important to examine.

For example, the largest percentage of the exonerated cases have DNA evidence at the centre of the investigation, Mr Yankah said.

The percentage of these types of cases that turn out to be wrong varies between two to ten per cent.

But, Mr Yankah said, “we have no reason not to believe” that the same issues that caused wrongful convictions in those cases - police and prosecutorial misconduct, false identifications, accusations, and confessions - could not also apply to cases that do not have DNA evidence at the centre of them.

That is when the numbers “turn out to be stunning” given that 2.3m people are currently incarcerated in the US, said Mr Yankah.