'Making a Murderer': Steven Avery pens letter from prison to supporters

Steven Avery has finally reached out to his supporters.

In a handwritten letter posted on Twitter by his new attorney, Kathleen Zellner, on Friday, the main subject of the wildly popular Netflix documentary true crime series maintained his innocence and asked that every possible forensics test be run on the evidence in the case.

"To my supports: I want every forensics test possible because I am innocent," Avery wrote.

Avery served 18 years in prison for a sexual assault conviction out of Manitowoc County, Wis., for which he was exonerated by DNA evidence in 2003. Then in 2005, Avery was convicted of the murder of 25-year-old Teresa Halbach. Avery's nephew, Brendan Dassey, was also convicted for the same murder. Dassey's lawyers argued his confession to authorities was coerced.

Click through images of Steven Avery's trial from "Making a Murderer":

Avery's original trial lawyers argued Avery was framed by local law enforcement; the attorneys did not accuse law enforcement of killing Halbach, but said authorities believed so strongly that Avery was guilty, they planted evidence to ensure a conviction.

Zellner also discussed Avery and his case to some degree when she appeared on Dateline NBC Friday.

"Generally, since 2007, there have been significant advances in forensic testing," Zellner told Dateline's Andrea Canning. "Am I going to tell you exactly what it is? I am not. But it's been a long time. There was a lot of evidence that wasn't tested."

Avery filed an appeal in early January requesting his conviction be thrown out due to a tainted jury and evidence in the case be mishandled by law enforcement.

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