Updated 10/30/14 – 1:38 p.m.

CHICAGO (CBS) — In another stunning reversal in a 1982 double murder, Cook County prosecutors have thrown out the conviction of 64-year-old Alstory Simon, whose videotaped confession freed Anthony Porter from death row in 1999, approximately 48 hours before Porter was to be executed.

A Cook County judge granted prosecutors’ request to order Simon’s immediate release from the Jacksonville Correctional Center on Thursday, after the Cook County State’s Attorney’s office asked to have Simon’s conviction vacated.

Upon leaving prison, Simon told reporters: “When I first came in here, I was very bitter. A person would say hello to me, and I would cuss them out and get in a fight, you know. Then I thought, I got to let that go.”

Simon confessed to the 1982 murders of Marilyn Green and her fiancé Jerry Hillard, but has since claimed he only confessed and pleaded guilty because he was told he’d serve a short time in prison, and would get rich from book and movie deals. He was sentenced to 37 years in prison, but later recanted.

Cook County State’s Attorney Anita Alvarez began reviewing Simon’s conviction last year, after he claimed his confession was coerced by private investigator Paul Ciolino, who was working for Northwestern University professor David Protess and the school’s Medill Innocence Project, which helped get Porter freed thanks to Simon’s confession.

Simon was released from the Jacksonville prison early Thursday afternoon. In a phone interview, Simon told WBBM Newsradio’s Steve Miller he got the news that he was being set free when he woke up Thursday morning.

“I was hoping and praying that this day would come sooner or later, because I am innocent, and I just thank God that Alvarez’s investigating team, after the investigation, recognized and saw that,” he said.

Simon blamed Protess, Ciolino, and Northwestern for the 15 years he has spent in prison.

“I was coerced into the confession. That confession was extracted by Paul Ciolino, with the use of threats and intimidation and guns … and monetary promises,” Simon said.

Simon said he had been smoking crack cocaine for three days and three nights before Ciolino questioned him, and put a gun to his head.

“When he put the gun to my head, and talking about we can do this the easy way or the hard way, I started thinking that ‘Well, hell, they’re going to shoot me in my head, and probably leave me here for dead, and claiming that when they came to question me about a homicide, I opened fire on them, and they had to kill me,” he said.

To hear Simon’s defense attorney, Terry Ekl, tell it, Protess and Ciolino saw Porter as a potential poster boy for the anti-death penalty movement, and needed someone else to take his place in prison.

“Porter was close to being executed for a, quote, ‘crime he didn’t commit.’ Porter was the lynchpin for a lot of the actions that subsequently occurred, so they were vested in finding someone to replace Porter as the person who did that murder,” Ekl said. “That’s what I think the motive; that’s my opinion, that was the motive behind this.”

Porter indeed became the impetus for abolishing the death penalty in Illinois.

Simon’s confession led to the Porter’s release in 1999, after he had served 17 years on death row, and had come within 48 hours of being executed. Then-Gov. George Ryan pardoned Porter within weeks of his release from prison. He placed a moratorium on all executions less than a year later. Eventually, he pardoned several other death row inmates, and commuted the sentences of every other person facing the death penalty to life in prison, citing extensive flaws in the system. In 2011, the state abolished the death penalty altogether.

Ekl said he was numb Thursday morning after learning prosecutors had agreed to clear Simon of the charges and set him free.

“We’ve been working for Alstory Simon for 10 years, and for a while, I never thought this day would come,” he said. “But we were increasingly encouraged over the last year, where Anita Alvarez and her staff conducted the reinvestigation of the case; and I just can’t say enough good things about the way her office handled this case, the thoroughness of their investigation. I always sensed they were trying to do the right thing, and come to the right result, and they did that today.”

Ekl said he’s convinced Porter is guilty of the murders.

“Shortly before this incident, he walked up to a man on the street who was sitting there with his dog, kicked the dog in the head, and then when the man protested, he shot the man in the head. That’s the type of person we’re talking about,” he said. “You guys ought to take a look at Anthony Porter’s rap sheet; all of the cases that he has been charged with, convicted on – intimidation of witnesses, etc. I wouldn’t believe a single thing that came out of the mouth of Anthony Porter, ever.”

Anthony Porter walks out of the Cook County Jail  on Feb. 5, 1999, after more than 16 years on death row.  A group of Northwestern University journalism students developed information that led to a Wisconsin man confessing on videotape to the 1982 double-murder for which Porter was imprisoned. (Photo credit: JOHN ZICH/AFP/Getty Images)

Anthony Porter walks out of the Cook County Jail on Feb. 5, 1999, after more than 16 years on death row. A group of Northwestern University journalism students developed information that led to a Wisconsin man confessing on videotape to the 1982 double-murder for which Porter was imprisoned. (Photo credit: JOHN ZICH/AFP/Getty Images)

Since he was pardoned for Hillard’s and Green’s murders, Porter has been back to jail or prison at least four times, on convictions for reckless conduct, resisting police, theft, and probation violation.

Prosecutors have not said if they believe Porter committed the murders, but he cannot be retried, as the U.S. Constitution protects him from double jeopardy.

Alvarez said Protess and Ciolini used “alarming tactics” in their efforts to clear Porter’s name, including having actor to speak to Simon, pretending to be a witness to the shootings.

Calling Ciolini a “rogue investigator to obtain Simon’s confession, she said he came to Simon’s home with “guns drawn,” posing as a police officer.

Alvarez said, to this day, some witnesses maintain Porter was the shooter, although she stopped short of saying she believes he was the killer.

The state’s attorney’s Conviction Integrity Unit began reviewing Simon’s case last October, and interviewed him twice this year. Both times, he said he was innocent.

Ekl said Protess and Ciolino used deception, threats, and false promises to get Simon to confess so they could get Porter set free.

“What essentially happened is Protess, Ciolino, and others decided it was more important to get Anthony Porter out of jail, and you may recall at time there was a lot of discussion about the anti-death penalty movement. Anthony Porter became essentially the poster boy for the anti-death penalty movement. I think they essentially framed Alstory Simon to get Anthony Porter out of jail so they had that poster boy,” he said.

Rob Warden, director emeritus of the Northwestern University Center on Wrongful Convictions, insisted the Medill Innocence Project — which was a part of the center when Protess started it in 1999 — got it right in getting Porter exonerated. He also said Simon’s conviction was correct, even though the charges have now been vacated and he’s being set free.

“Not only did he confess to the crime on videotape, but he then proceeded months later to plead guilty in open court, and to apologize to the families of the victims,” Warden said.

Warden also said Simon’s ex-wife Inez Jackson claimed Simon was the killer. He said there was no reason to convict Porter of the murders, and no reason to exonerate Simon.

Ekl said it’s not unusual for a suspect to confess to a crime he did not commit, noting Illinois has seen many murder convictions tossed out because a defendant’s confession was coerced.

“This is a very, very complicated and confusing case; and there once was a time when all of us thought that people did not confess to things they didn’t do. We now know that’s not true, so the whole set of circumstances surrounding this case are far beyond what you would call a standard confession, where a person is admitting what they did. So it was an extraordinary case,” he said.

Now that he’s free, Simon said he plans to spend “a lot of quality time with my family.”

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