Making a Murderer's Steven Avery has spent years in jail. Now someone else has 'confessed'.

The case behind the worldwide Netflix phenomenon, Making a Murderer, has been dealt a huge twist, with another prison inmate reportedly confessing to the murder of Teresa Halbach.

Steven Avery, and his nephew Brendan Dassey, have been behind bars for more than a decade for the 25-year-old photographer’s rape and killing, but both to this day maintain their innocence.

The documentary into their conviction turned the world into armchair detectives in 2015, sending the little-know murder trial from Manitowoc County Wisconsin into a global phenomenon.

Here’s the original Making A Murderer trailer to refresh your memory. Post continues after video. 

After the success of series one and two, an unaffiliated spin-off series Convicting a Murderer went into production.

During a taped interview with the crew, an unidentified prisoner allegedly confessed to the crime.

The series’ director Shawn Rech told Newsweek they handed the recording over to police and are waiting to hear what investigators think about it.

“Seeing as it was given by a notable convicted murderer from Wisconsin, we feel responsible to deliver any and all possible evidence to law enforcement and legal teams,” he told the publication.

The team have been in production for 20 months and say they’ve gained “an unfathomable amount of information and evidence”.

Let’s see. You be the judge of the credibility of this confession.#MakingaMurderer #TruthWins pic.twitter.com/NOEJtrrmb3

— Kathleen Zellner (@ZellnerLaw) September 24, 2019

Rech says he felt compelled to further dig into the cases after watching the first two series and told Newsweek, “After doing a little bit of follow-up research I learned that not only did I not have the whole story, but I was misled by the series. And I’m saying this as a fan, not as an established documentary filmmaker”.

The story of Avery and Dassey gripped true crime fans because of Avery’s complicated criminal history. He served 18 years in prison for the wrongful conviction of sexual assault and attempted murder of Penny Beernsten in 1985.

Then, in 2005, he was charged with the murder of Halbach, and convicted during a nine-day trial in 2007.

The global audience has been split pretty much down the middle, with many believing he was once again wrongly convicted. But the courts have remained firm, and as recently as 2017 a judge denied Avery a new trial.

Dassey was originally interviewed as a witness in the crime, but was arrested after his cousin said he discussed the murder with her. Under police interrogation he confessed in detail to helping his uncle carry out the rape, killing and dismemberment of Halbach.

Much of the footage shown within the documentary brought Dassey's admission of guilt into question due to the coercive tactics used by an investigator, Dassey's low IQ and the then 15-year-old's young age at the time of the crime.

Almost immediately after confessing, Dassey recounted and reclaimed his innocence and has been fighting for freedom ever since.

Avery has always maintained his innocence, claiming he was framed by police. Much of Making a Murderer season one focused on the theory that a Manitowoc investigator planted Avery's blood - from a vial - in Halbach's car.

With this new startling alleged confession now thrown into the mix, Dassey and Avery are once again in the spotlight. If found to be true, this confession will see them walk free after 12 years behind bars.

The documentary that produced the confession is expected to air in 2020.