Since 1991, 29 Missouri men and women have walked free from prison. Most were never supposed to see outside the prison walls again.

Missouri courts are releasing prisoners at higher rates now than at any other time in recent history.

Last week, Ryan Ferguson became the sixth person released early from a state prison in the past year.

He joins a small, but growing group, in Missouri. George Allen Jr., Reginald Griffin, Paula Hall, Robert Nelson, Mark Woodworth and Ryan Ferguson all faced decades behind bars until this year.

"This is not an anomaly, look at other cases and know this is a part of our justice system and there are other innocent people in prison," Ferguson said after his release from prison.

"I think that people think that these cases are just anomalies, that they happen just once in a blue moon," said Laura O'Sullivan, a law professor at the University of Missouri-Kansas City.

O'Sullivan teaches students about wrongful conviction cases and theory.

"One of the very first things I tell them is, 'When you look at these cases initially, you'll think that they look guilty. Because often times, 12 jurors look at the case and think that they look guilty,'" she said. "But I think what we're finding out is, it's a much bigger problem than we ever imagined."

And if it's a problem, it's becoming a more common one.

In 1989, 20 people nationwide walked free. This year, that number has grown to 77.

O'Sullivan says researchers look at a few reasons, including official misconduct, false confessions, faulty informant and eyewitness testimony, and bad science.

"I think because of the better tech, we're able to get to the information and evidence that will help us reveal the injustices that have occurred," she said.

The National Registry of Exonerations is run by Michigan and Northwestern law schools. It consists of pages that include summaries of cases that never should have happened.

On Missouri's page, users will now find Ryan Ferguson, in addition to Joshua Kezer.

"It is necessary, we're talking about innocent lives," said Kezer, who was exonerated in 2009. "This isn't a numbers game, these aren't animals, this isn't throwaway material. This is human life."

Kezer was exonerated after spending 15 years in prison for a southeast Missouri murder he says he did not commit. Now, the Scott County sheriff agrees with him.

Kezer talked with ABC 17 News the day after Ferguson's convictions were thrown out.

"It's a shock the day that it comes because you know it's going to come, you don't know when, you don't know how, you know, what circumstance or what motion or something of that nature," he said.

Since gaining freedom, Kezer has been outspoken about helping others to do the same.

One of the first people he named was Ryan Ferguson. And just last week, Ferguson named another.

"Charles Erickson," Ferguson said. "He's many things, but one thing we know he his, is he's innocent."

"We know that Charles Erickson is innocent, we know that," O'Sullivan said.

O'Sullivan is the senior counsel for the Midwest Innocence Project and now the attorney for Charles Erickson.

"We're only halfway there," she said.  "Fifty percent justice is not justice enough. Charles deserves to be released."

Her last client, Robert Nelson, was released in 2013 after nearly 30 years in prison. George Allen got out after two decades. Joshua Kezer served 15 years. And Ryan Ferguson was behind bars for eight years.