Convicted Killer Steven Avery Will One Day Walk Free Thanks to 'Explosive Evidence,' Attorney Vows

Netflix's Making a Murderer, which returns for part 2 on Friday, cast a harsh light on the case against Steven Avery and Brendan Dassey in Teresa Halbach's death

Since its premiere nearly three years ago, Netflix’s docuseries Making a Murderer has raised more doubts about the death of Teresa Halbach and who was responsible than it has provided answers.

But one person not gripped by uncertainty is Kathleen Zellner, an attorney famous for exonerating wrongfully convicted people who, since January 2016, has been representing Halbach’s convicted killer Steven Avery.

Making a Murderer — which returns for part 2 on Friday (an exclusive preview is above) — cast a harsh light on the case against Avery and his teenage nephew Brendan Dassey, both of whom were found guilty of murdering Halbach, a 25-year-old photographer, in October 2005.

Avery and Dassey have maintained their innocence for years, and Making a Murderer‘s new batch of episodes will follow their push for freedom — as prosecutors fight just as hard to keep them behind bars, confident, as were two juries, that the killers are behind bars.

Halbach’s family, who declined to participate in the series, has dismissed it as exploitative and one-sided. Aunt Kay Giordana told PEOPLE in 2016 that she had “no doubt” about Avery’s guilt.

Zellner feels just as strongly about his innocence. As Avery’s appellate attorney, she has made it her mission to re-investigate the case against him and pull it apart at the seams.

• For more on Making a Murderer part 2 and what has changed in the case in the last three years, subscribe now to PEOPLE or pick up this week’s issue, on newsstands Friday.

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Making a Murderer‘s filmmaking team, Moira Demos and Laura Ricciardi, call Zellner the “primary engine of the story” in part 2 and they closely followed her work: calling on experts to re-examine the forensic evidence (such as blood and DNA found on Halbach’s vehicle and her burned remains found on the Avery property) and hunting for clues about other possible suspects.

In an exclusive interview with PEOPLE, Zellner maintains her work has uncovered “big, explosive evidence,” some of which she has already cited in public court filings. Among other arguments, she cites experts who cast doubt on the prosecution’s interpretation of forensic evidence, including the finding that Halbach was burned where her remains were found. Zellner also contends that prosecutors previously withheld evidence from the defense.

RELATED VIDEO: Attorney For Making a Murderer’s Steven Avery Wants New Trial, Points Finger at Victim’s Ex

The court has yet to rule in her favor, but Zellner is not discouraged.

“We believe the case will ultimately collapse when it gets to the higher courts within Wisconsin,” she says.

Where the initial murder investigation was, officially, a fact-finding mission, the post-conviction phase can seem largely about process and interpretation — a hunt for errors. What does the underlying evidence really mean and was it analyzed correctly? Were the rules followed? What may have been overlooked?

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Halbach Family/Herald Times Reporter/AP Photo

What’s Next?

As ever, Avery — who was famously wrongfully convicted for a rape he didn’t commit decades before Halbach was killed — remains a Rorschach test depending on one’s opinion of his case: His insistence on his innocence is either exactly what an innocent man would say or the purest proof of his evil.

Whatever happens, a resolution will not be quick. Avery, 56, is still “at the beginning” of his appellate process, which will take another 18 to 24 months to work its way through state court, according to Zellner, who is preparing to file a brief in the fall.

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Dassey, now 28, has fewer options. After a federal judge agreed in 2016 that his confession was coerced and he should be granted a new trial, a higher court reversed that ruling and, in June, the U.S. Supreme Court declined to take up the issue.

Dassey’s next move has not been announced, though he could seek clemency or find new evidence of a violation of his rights. His longtime attorneys, Steven Drizin and Laura Nirider, tell PEOPLE they are “continuing to fight for him.”

AP Photo/The Post-Crescent, Dan Powers

Avery remains optimistic about his future, according to Zellner. His certainty mirrors her.

“He will die in prison before he would ever take a deal,” she says, continuing:

“That’s why I’m so positive that he’s innocent. … That’s the strongest characteristic of someone who’s innocent: They’ll die in prison before they will admit guilt, and that’s Steven Avery.”