Steven Avery, the Wisconsin man whose conviction for rape and murder was the subject of hit Netflix documentary 'Making a Murderer,' says he will soon be free thanks to new evidence.

Speaking to In Touch magazine from prison, Avery, 54 - who was convicted in 2007 alongside nephew Brendan Dassey, 26, for the 2005 killing of Teresa Halbach was certain he would be free.

'I'm going to be free,' he said, referring to his appeal, which will be filed on August 29. Dassey's conviction was overturned Friday.

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Convicted: Steven Avery is seen here (right) in his 2007 trial for the rape and murder of photographer Teresa Halbach. He was found guilty, along with nephew Brendan Dassey

Overturned: A judge overturned the conviction of Dassey (center) Friday, saying he was coerced by detectives. Avery is filing an appeal on August 29, citing new evidence

'I thought sooner or later (this day) would (come),' said Avery. 'The truth is coming out.'

One vital piece of evidence in the appeal being filed by Avery's new lawyer, Kathleen Zellner, centers on the sample of Avery's blood found in Halbach's car, a source told In Touch.

'There's strong scientific evidence that the blood found in Teresa's car was planted by using a cotton swab,' the source said.

Avery's previous legal team contended that Manitowoc County police had framed Avery for murder because he was suing them and the county over his wrongful conviction for rape and attempted murder in 1985.

Victim: A key piece of evidence in Halbach's (pictured) case was Avery's blood being found in her car. But his lawyer says she has evidence it was planted

A key moment in the documentary shows his former lawyers learning that a vial of Avery's blood, being held by police as evidence from that case, had been opened and apparently pierced with a needle.

Retired NYPD detective Hal Sherman told In Touch that if the defense can prove forensic teams took blood samples from the car with a synthetic swab, then the cotton fibers found in the blood would prove tampering.

If they cannot, however, then it proves nothing.

The source also says that Zellner can prove the blood in the car was too old to be fresh - again suggesting it came from the 1985 sample - but experts say there's no way to tell that.

Avery's hopes for release have been buoyed up by Dassey's conviction being overturned on Friday, after Judge William Duffin said the boy's confession was coerced.

Dassey was just 16 when he was interviewed, but has a mental age of nine. Footage appears to show police railroading him into a confession and feeding him information that he later admits to.

'Proof': She says cotton fibers in the blood show it was taken from an earlier evidence sample, which was taken when Avery was wrongfully convicted for rape in 1985

Avery told In Touch that he hopes people will believe his claim that he was framed.

'Hopefully more people understand (that I was framed) because of the judge's decision,' he said. 'He has seen through all of that.'

'I'm 1,000 per cent confident that I'll be free,' he promised.

Support for Avery's release has been growing since the release of 'Making a Murderer' on Netflix in December last year.

The full interview with Avery is featured in In Touch's August 29 issue.