Two North Carolina men who have been behind bars for 30 years, one of them on death row, will go before a judge on Tuesday morning to present new DNA evidence of their innocence of the murder and rape for which they were convicted as teenagers in 1984.

Lawyers representing Henry McCollum, who faces execution, and his half-brother Leon Brown, serving a life sentence for the brutal 1983 killing of an 11-year-old girl, will call for the pair to be released and cleared of all convictions. They will show the court recent DNA test results that exclude both men as the source of biological material gathered at the crime scene but record a positive match to the genetic profile of another man who has a long criminal record for sexual offences in the area.

The other man, Roscoe Artis, is serving a life sentence for a separate yet remarkably similar rape and murder that occurred in the same small town of Red Springs three weeks after McCollum and Brown were arrested. Artis was living at the time a few hundred feet from the field in which the body of the 11-year-old girl, Sabrina Buie, was found.

The hearing, which is scheduled to last several days, is the first major opportunity for McCollum, now 50, and Brown, 46, to prove the innocence they have always professed. Brown’s attorney, James Payne, said they were hopeful that at the very least both men will be released pending a new trial, though he added that in his view the DNA evidence was strong enough to have them immediately exonerated.

His co-counsel Ann Kirby said: “This case highlights in a most dramatic manner the importance of finding the truth.”

The events that would put the two teenagers behind bars for three decades began on 24 September 1983, when Sabrina Buie went missing. A couple of days later her body was found in a field of soya beans behind a grocery store in Red Springs, a small town of just 3,000 people in the south of the state. Forensic tests showed she had been raped and suffocated, with her underwear having been forced down her throat with two sticks.

A day after Buie’s body was found, Brown, then just 15, and McCollum, 19, were arrested by detectives acting on a tip from a “confidential informant” who later turned out to be a 17-year-old girl at their school who had heard rumours they were involved in the crime. Both boys were intellectually disabled, Brown so severely so that he could barely read or write.

After police interrogations lasting several hours, both boys signed confessions that had been written for them by detectives of Red Springs police department. In the confessions, they separately implicated each other and three other boys who had allegedly been their accomplices.

Yet when police came to investigate the movements of the three other boys, they found that they had watertight alibis. No charges were ever brought against them.

Payne told the Guardian the confession that Brown signed was riddled with inconsistencies. “It was inconsistent with the physical evidence, with the facts of the case, with his brother’s confession, and it contained details that were known by the police officers interrogating him at the time. When you combine that with the DNA evidence that we now have, it makes a very bold statement that both my client’s and McCollum’s confessions were false.”

At no point over the past 30 years has any physical or forensic evidence been produced to directly connect either man to Buie’s rape and murder. DNA testing was not available at the time of the original trial, and it is only in recent years that investigators have applied genetic testing techniques to biological evidence gathered at the crime scene.

The breakthrough came with the decision of the North Carolina Innocence Inquiry Commission to take on the cases of Brown and McCollum. The commission is an independent fact-finding body that has been invested by the North Carolina general assembly with full state powers to subpoena witnesses and evidence as well as the statutory authority to carry out DNA testing.

The executive director of the commission, Kendra Montgomery-Blinn, confirmed to the Guardian that extensive DNA testing had been conducted as part of an active and ongoing investigation.

Court documents show the results of the DNA testing that the commission ordered on materials gathered at the scene of Buie’s murder. All the items tested – including her panties and other items of clothes, hairs collected from her shoes, sticks used in the killing, three Schlitz Malt Liquor cans and the butt of a Newport cigarette – excluded McCollum or Brown. However, the tests did manage to produce a partial DNA profile from the cigarette butt that was consistent with having come from an unidentified male.

At the commission’s request, that DNA profile was then put through the national DNA database, known as CODIS, and in July a positive match was attained, connecting the cigarette butt to Roscoe Artis. When lawyers began looking into the life history of Artis, they discovered startling details.

Artis had a history of sexual assaults dating back to 1957. He is currently in prison on a life sentence for the murder of a young woman, Joann Brockman, on 22 October 1983, less than a month after Sabrina Buie died. Like Buie, Brockman was killed in Red Springs, and like her the cause of death was asphyxia due to manual strangulation.

Court documents record that Artis lived at the time of the murders with his sister in a house that was located a matter of feet from the field in which Buie’s body was found. Court filings also record that Artis has made statements to a former fellow prison inmate and to staff of the commission that he knows as a certainty that Brown and McCollum were not involved in the Buie murder.

The strength of the DNA evidence is such that even the present district attorney for Robeson County, Johnson Britt, is not opposing calls for Brown and McCollum to be released.

“The whole case rests on the confessions and the DNA evidence threw those confessions under the bus,” Britt told the Raleigh News Observer.

False confessions have been found to be a major source of faulty convictions. Research by the Innocence Project has found that in almost a third of DNA exoneration cases, innocent people incriminated themselves or made outright confessions to the crime.

Factors behind such false confessions include intellectual disability, youth and ignorance of the law – all of which applied in the cases of Brown and McCollum.

The Red Springs police department is likely to face some difficult questions at Tuesday’s hearing. Detectives who carried out the original interrogation of the two defendants in 1983 are accused in court documents of having added key crime scene details, such as the brand of the Newport cigarette butts that were found, into the boys’ “confessions” which they wrote for them.

Also serious are suggestions that the police department has failed to disclose vital evidence to prosecutors or to defence lawyers as recently as this year. Over the years, the police department has consistently denied having retained any evidence relevant to the case.

Yet only last month investigators with the North Carolina Innocence Inquiry Commission discovered a box full of potentially critical physical evidence at police headquarters; it was seized using statutory powers. The box, which had been stored by Red Springs police department since the early 1990s, contained clippings of Sabrina Buie’s hair and nails and a beer can and gum wrapper found at the crime scene.

In a court filing, Brown’s lawyers write that “from 1984 until 2014, the Red Springs police department was in possession of exculpatory evidence which is material to Leon Brown’s innocence. The Red Springs police department withheld exculpatory evidence from the state and from Leon Brown and his attorneys.”

In a final twist, it has also recently come to light as a result of the commission’s work that two fingerprints were discovered on a beer can found at the scene of Buie’s rape and murder. One of the prints belonged to Buie herself, while the source of the other print was unknown.

In the course of its investigations, the commission learned that on 5 October 1984, just three days before the trial of Brown and McCollum began, the Red Springs police department submitted a request to a forensic laboratory asking for the unidentified fingerprint to be compared with those of Roscoe Artis. On the same day, however, the request for a fingerprint comparison was cancelled without explanation. The existence of the print was never disclosed either to prosecutors or to defence lawyers acting for the two boys.

The Guardian understands that the unidentified fingerprint remains in the possession of the authorities and has never been tested to determine its source.