Zellner told the magazine that the investigation's focus was kept narrowly on the families of Avery, his convicted nephew Brendan Dassey, and Halbach's family. She says key people who knew the victim were overlooked.
"We've got access to documents the public doesn't have," Zellner said. "We've got all the police reports, we can see exactly what they did and did not do. And it's a lot more about what they did not do."
In the months since she took Avery on as a client, Zellner has combed through all the documents in the case and performed or ordered her own forensic tests completed.
In Halbach's phone records, Zellner discovered that the victim had made two calls a couple of days before she was killed to a man with a record of sexual-abuse crimes in Arizona.
"A well-trained investigator, they'd be all over that," Zellner said. "And they would have gone and talked to [that man], and they would have interviewed these other people that [Teresa Halbach was] talking to right before her death. She's like prey being stalked, and that's [the most likely type of] person who would have been after her."
As Business Insider previously reported, Zellner found something else in the phone records that she thought was her biggest proof of Avery's innocence. Judging by the location of her last cellphone call based on cell-tower data, Halbach had left the Avery auto yard, and Avery's phone records show that he didn't leave the property, according to the lawyer.
Zellner faults Avery's previous legal team, Jerry Buting and Dean Strang, for not using this information during his trial.
"They screwed it up," she said.
In response to Zellner's critique of their work, Strang told the magazine, "That she is criticizing some aspects of the work I did at trial means that she is doing her job." Buting declined to comment on Zellner's critique but did say, "I continue to hope that Steven Avery gets a new trial."