The University of Michigan's National Registry of Exonerations announced in a report released Tuesday that a record 125 people across the United States were in 2014 exonerated of crimes they were falsely convicted of, beating 2013's 91 people.

Much of the increase came from Texas, where investigators freed 33 people falsely convicted of drug offenses in Harris County (Houston). Other people were exonerated thanks to increased use of "prosecutorial Conviction Integrity Units," special investigative teams which review convictions and discovered 59 innocent people in prison in 2014 alone.

How is this happening? It basically turns out that the number of people exonerated increases the more the government actually makes an effort to look for them. From 1989 to 2014, the NRE recorded 1,535 exonerations, with a clear upward trend over time.

NRE

Aggressive law-enforcement and prosecutorial tactics appear to play a role, too: 47 of the 125 exonerees had pled guilty to the crimes they were accused of, while about 46% had been sentenced for crimes that had never been committed in the first place.

Just 13% of non-drug-related crimes involved a suspect that had pled guilty at trial. That's likely because prosecutors routinely threaten defendants facing drug charges with what Human Rights Watch calls "extraordinarily severe prison sentences," forcing them into plea deals. In Harris County, all 33 drug convicts were found to have committed no crime at all.

DNA evidence has not played a major role, remaining at average levels.

"The big story for the year is that more prosecutors are working hard to identify and investigate claims of innocence," author and Michigan law professor Samuel Gross said in a statement. "And many more innocent defendants were exonerated after pleading guilty to crimes they did not commit."

NRE

How many innocent people are there? It's hard to tell. The Innocent Project estimates that between 2.3% and 5% of all prisoners in the country are innocent, and since the U.S. has the highest incarceration rate in the world, with an estimated 2.4 million state, federal and county prisoners in 2014, that would mean somewhere between 55,000 and 120,000 of them were innocent.

Other researchers have pegged the number of innocent death row prisoners at about 4.1%, or one in 25, with the actual innocence rate among the many prisoners serving long-term sentences even higher. By that metric, the U.S. has likely sentenced over 200 innocent people to death since 1978.

There are just 15 Conviction Integrity Units around the country, which have so far generated 90 exonerations since 2003 (according to the NRE, more than half of which happened in 2014). There's no telling what would happen if every jurisdiction had a CIU, but the U.S. locks up an awful lot of people, so there would probably be more than enough suspect cases to keep them busy.

That's not even considering the extraordinarily long prison sentences many convicted offenders receive, often for relatively minor crimes. According to MSNBC, one-quarter of the Justice Department's budget now goes to the costs of locking up non-violent prisoners.

Why you should care: Not only does the U.S. have the highest incarceration rate in the world and harsh sentencing practices, it turns out that a significant number of the people languishing in jail might not have even committed a crime in the first place.

Record numbers of exonerations are good news. It shows that many of the falsely convicted are receiving more attention than they would have previously. But it looks like there's still a lot of digging around in old case files to do, and many innocent people still in jail.