Sycamore, Illinois (CNN) Cheers erupted in the courtroom nearly four years ago when a judge found Jack McCullough guilty of the 1957 kidnapping and murder of Maria Ridulph. Many believed that the bogeyman who stole the 7-year-old -- and this community's sense of innocence and safety -- had finally been brought to justice.

But on Friday, a prosecutor will tell a judge for the third time in as many weeks that McCullough is innocent . He will join McCullough's lawyers in asking Judge William Brady to throw out the conviction. And then the prosecutor, Richard Schmack, will move to dismiss the case, he has said, allowing McCullough to go free.

McCullough, now 76, was convicted of murder and sentenced to life in prison in 2012; an Illinois appeals court upheld the conviction last year.

But that conviction, Schamck insists, was based on false testimony, improper legal rulings controlling the evidence presented, and a timeline that was tweaked some 50 years after the fact to rule out McCullough's alibi.

McCullough has long insisted that he couldn't possibly have abducted and killed the child because he was 40 miles away in Rockford, Illinois, talking to recruiters and trying to enlist in the U.S. Air Force.

Schmack, the DeKalb County state's attorney, inherited the case from predecessor Clay Campbell. He took a second look at the evidence as McCullough pushed ahead with a last-ditch appeal. The jailhouse motion, written by hand in neat block letters, said police and prosecutors buried evidence supporting his alibi.

Schmack launched a six-month investigation that included a review of some 4,500 pages of documents -- old police and FBI reports, grand jury transcripts, trial transcripts, affidavits for search and arrest warrants, and even CNN's five-part series on the case, "Taken," which raised questions about whether the courtroom reconstruction of history was unfairly one-sided.

Schmack concluded that he'd found "clear and convincing evidence" that McCullough had been convicted of a crime he didn't commit.

The prosecutor subpoenaed records from AT&T and found that a collect call had indeed been placed at 6:57 p.m. to McCullough's home in Sycamore from a pay phone at the post office in downtown Rockford on on December 3, 1957-- just as McCullough said he had done. Schmack also built a timeline based on the statements of 21 people -- Maria Ridulph's family members, friends, neighbors and passersby -- that confirmed the FBI's original timeline ruling McCullough out as a suspect.

Maria Ridulph was taken from a street corner in Sycamore, Illinois, in December 1957.

Maria was taken that day some time between 6:45 and 7 p.m. -- and not as early as 6 p.m., as alleged during McCullough's trial.

It would have been impossible for him to have been in two places at once.

Schmack's timeline was framed around one indisputable fact: the 6:57 p.m. phone call. And he worked to pin down the last time Maria was seen on the corner of Center Cross Street and Archie Place. She had accepted two piggyback rides from a young man who gave his name as "Johnny," and had retrieved a doll to show him. When playmate Kathy Sigman returned from a quick trip home to fetch her mittens, she said, both Maria and Johnny were gone.

Family members and friends recalled in 1957 that they were watching "Cheyenne" and "Name That Tune" -- television shows that began at 6:30 p.m.-- while the girls played outside on the corner. And so, Schmack says, it was impossible that Maria was taken before 6:30.

Maria's mother, Frances Ridulph, drove to the Sycamore police station and reported her daughter missing at 8:10 p.m. Some 600 people searched through the night for the girl, and the FBI took over the case the next morning. Maria's body was found 144 days later, under a fallen tree more than 100 miles from Sycamore.

McCullough's new lawyers, who are defending him without compensation, initially sought a new trial. They asked for the chance to retry the case with the benefit of all the evidence, including 1957 FBI reports that show he was cleared after his alibi checked out. The FBI reports had been barred from his trial as inadmissible "hearsay." But, as an appeals court found, they could have come in as "ancient documents" because they are more than 20 years old. Still, the appeals court upheld McCullough's murder conviction, saying that the ruling barring the reports was "harmless error" that would not have affected the outcome of the trial. (It reversed the convictions for kidnapping and abduction of an infant because of legal technicalities unrelated to the judge's rulings on the evidence.)

But as Friday's hearing approached, McCullough's lawyers also asked for a finding of innocence and his immediate release. They noted in court papers that the request is unopposed.

Prosecutor Richard Schmack reviewed the conviction and wants McCullough freed.

In court papers filed earlier this week, Schmack asked Brady to find McCullough "factually innocent." Barring any unforeseen twists -- and this case has been full of them -- McCullough could walk out of the courthouse a free man, once again cloaked in the presumption of innocence, his lawyers say.

Chicago attorneys Gabe Fuentes and Shaun Van Horn joined the defense late last month. Earlier this week, they filed their formal appeal, giving it a weighty title: "Amended post-conviction petition demonstrating actual innocence."

It relies heavily on Schmack's findings: "Newly discovered evidence has emerged to corroborate his Rockford alibi and to show the falsity of the evidence offered by the state about the time of the abduction in Sycamore," they stated in court filings. "The FBI accurately concluded, following an extensive and thorough investigation in 1957, that Maria Ridulph was abducted near the corner of Center Cross and Archie in Sycamore, Illinois, between 6:45 and 7 p.m. on December 3, 1957."

The state's theory that the girl was kidnapped earlier was pure conjecture, McCullough's lawyers insist. "There was not then, nor is there now, a reasonable hypothesis for, or evidence supporting, an earlier time for the abduction" in any of the police and FBI reports from 1957-58.

"The FBI accurately concluded in 1957 that it is an absolute physical impossibility for anyone to have placed a collect call from inside this public building in Rockford at 6:57 p.m. and also to have participated in the abduction of Maria Ridulph in Sycamore, and there was nothing incorrect in their conclusion that (McCullough) was not involved."

Rather than challenging the assertion, as a prosecutor would in almost any other case, Schmack joined McCullough's lawyers in asking Brady to throw out the conviction.

He said he believes McCullough is innocent and won't be seeking to retry him. Instead, his court papers state he will dismiss the case with prejudice, meaning the charges can't be brought again.

Charles Ridulph, the slain girl's brother, explains why he's requesting a special prosecutor.

Charles Ridulph, the slain girl's older brother, filed a last-minute request for a continuance. He said an attorney he recently hired can't be in Sycamore for the hearing. He is seeking appointment of a special prosecutor.

Ridulph has accused Schmack of "abandoning" Maria, just as her killer abandoned her in the woods. He has said the prosecutor is acting more like a defense attorney.

But McCullough's lawyers, while expressing empathy for Ridulph, insist in court filings that he has no standing under Illinois law to make the special prosecutor request. Special prosecutors are appointed only if a prosecutor has a conflict of interest, either financially or personally.

A special prosecutor can't be appointed simply because a victim's family disagrees with the decision, they said.

"Despite the understandable grief that Mr. Ridulph feels for the loss of his sister and emotional turmoil that the discovery of Mr. McCullough's innocence has caused him, Petitioner Jack D. McCullough's life and freedom are at stake amid the prosecutor's conclusion of his actual innocence," his lawyers wrote.

Brady has indicated that he won't be rushed in his decision since the circumstances surrounding the case are so unusual that there's no legal precedent for him to follow.

"I have some obligation to make sure I understand the position of both parties," Brady said at the last court hearing, on April 1. "I don't just have your opinion or your client's opinion, and the state's opinion. I also have the opinion of a trial judge and an appellate court. I think it's premature for me to start commenting on what I think about any of that."