Avery and his nephew Brendan Dassey were convicted of Ms Halbach’s murder in 2007. Both have maintained their innocence.
On Monday, wrongful conviction lawyer Kathleen Zellner, who featured in season two of the Netflix true crime series, filed what’s a known as a Brady motion with Manitowoc County Court in Wisconsin.
The motion claims a former newspaper delivery driver named Thomas Sowinski saw Avery’s other nephew, Bobby Dassey, and an unidentified older man, “suspiciously pushing”, Ms Halbach’s Toyota RAV-4 down Avery Road towards the family’s junkyard.
The alleged sighting came days after her disappearance on October 31, 2005.
“The new witness affidavit is the first eyewitness observation ever reported in the case,” Ms Zellner told 9news.com.au in a statement.
“(It) corroborates our theory that Steven Avery was framed.
“It also links Bobby Dassey, the state’s star witness to the murder to Teresa Halbach.”
The driver has signed an affidavit saying he informed Manitowoc Sheriff’s Office at the time of Ms Halbach’s disappearance, but he was never contacted for more information.
Ms Zellner said tips “are flooding in” regarding the identity of the other man.
“Thank you for all the tips on the accomplice. We should have him identified very quickly,” she wrote on Twitter.
Ms Halbach vanished on October 31, 2005 after visiting Avery’s home to photograph a car he intended to sell.
While searching for the 25-year-old police found her Toyota RAV4 hidden in a salvage yard not far from Avery’s home.
Avery’s DNA was found inside Halbach’s vehicle.
Her charred remains were later discovered in a fire pit on the property.
Avery was in the midst of a A$47 million lawsuit against Manitowoc County when he was convicted of Ms Halbach’s murder.
He was suing the county after being wrongfully convicted of rape.
He served 18 years before being exonerated by DNA evidence in 2003.