John Ferak

USA TODAY NETWORK-Wisconsin

Legal observers keeping an eye on attorney Kathleen Zellner's strategy to get Steven Avery exonerated in the murder of Teresa Halbach might want to brush up on a 1990s double murder case in Kewaunee County.

There was no physical evidence and no eyewitnesses to tie Beth LaBatte to the Nov. 16, 1991, gruesome murders of two retired schoolteachers in Kewaunee County — just jailhouse snitches.

At LaBatte's 1997 murder trial that was moved to Appleton, three prisoners testified that LaBatte confessed to killing the Cadigan sisters — Ann, 90, and Ceil, 85 — in their Casco home. The jury found her guilty. Although LaBatte professed her innocence at sentencing, the Outagamie County judge ordered the Green Bay woman to serve two life sentences, calling her evil.

Years later, the Wisconsin Innocence Project entered the case.

In 2006, after nearly a decade of wrongful incarceration, LaBatte was set free.

The Wisconsin Innocence Project had used a conventional post-conviction maneuver — the pursuit of advanced DNA tests — in trying to overturn LaBatte's murder convictions.

It worked. Several significant clues left at the crime scene, including a broken pool cue, did not contain LaBatte's DNA.

Instead, the DNA residue pointed to a still-unknown male attacker. LaBatte's legal advocacy team had no obligation to prove to the court the real killer's identity. Incidentally, a decade later, the double murders remain unsolved.

Thirty miles away, at the Manitowoc County Courthouse, the lawyer representing Avery has taken a bolder, riskier legal stance.

Zellner, an attorney from suburban Chicago, plans to present irrefutable scientific evidence to point the finger at someone other than Avery and his nephew Brendan Dassey for the murder of Halbach. The 25-year-old photographer from Green Bay vanished without a trace on the afternoon of Halloween 2005 after visiting the Avery Salvage Yard, a place she had been numerous times.

"Mr. Avery's trial transcripts reveal that certain relevant evidence collected in his case was never subjected to prior testing," Zellner stated in last month's legal filing. "If these items such as the blinker light, hood prop and battery cable are tested, they could conclusively demonstrate Mr. Avery's innocence by identifying the real perpetrator's DNA."

Two experienced criminal defense lawyers told USA TODAY NETWORK-Wisconsin that Zellner's legal strategy of trying to prove somebody else is the killer is unnecessary to overturn her client's conviction. The LaBatte case speaks to that. However, Zellner's tactic makes sense given the worldwide attention the Avery case has generated in the wake of the Netflix series, "Making a Murderer."

"The Holy Grail is to find an alternative suspect," suggested Daniel Medwed, law professor at Northeastern University in Boston. "Developing the case of a plausible other suspect after the trial ... it's about showing new evidence that creates a probability of a different result. For every crime, there is a true perpetrator who is out there."

Zellner has made it clear in past media interviews that she is not interested in winning a new trial for Avery. She wants to deliver his exoneration without the need for a retrial. For now, Avery, 54, remains at the maximum security prison in Waupun. He's been in custody for the Halbach slaying since November 2005.

"To some, if you are aiming for the king, you better kill the king," Medwed told USA TODAY NETWORK-Wisconsin. "The challenge for Zellner is not just to find all those holes in the case against Avery but ... it's all about an alternative narrative of the case. She's an exceptional lawyer, and this is exactly what I would do. Going forward, as DNA cases diminish across the country, Kathleen Zellner's approach will become more popular."

But Zellner's path toward exoneration won't be easy, Medwed said.

The tactic poses substantial risks and high margins of error, the Boston legal scholar noted. Statistics bear out that only a fraction of all murder convictions get overturned on appeal. There's a natural tendency for the courts to presume that the convicted murderer committed the crime, based on evidence presented at trial.

Therefore, investigating every viable third-party murder suspect in the Halbach case "is a complicated puzzle," Medwed said.

"If you're going to pursue alternative suspect angles, if it does not seem credible, then you risk that the judge will think you're grasping at straws," he said. "It's a risk-reward. The risk is that you're almost playing prosecutor. The payoff is enormous, but the risk of shooting and missing is huge."

And if Zellner backfires on developing her alternative suspect, she will most certainly jeopardize Avery's prospects of overturning his 2007 murder conviction.

"The more you can show someone else did it, the greater the chances you have of prevailing," Medwed said. But "just because there's enough smoke, it doesn't mean she will win. But it's a case absolutely worth pursuing ... and she's well-regarded."

Joe Nigro, Lancaster County public defender in Lincoln, Neb., said there's an expectation in cases involving claims of a wrongful conviction that the lawyers will present credible evidence that someone else got away with the crime.

Nigro supports Zellner's strategy of thoroughly investigating other possible suspects in Halbach's death.

"I think it certainly makes sense to explore it," said Nigro, who has more than 30 years in criminal defense work.

Moreover, pursuing advanced scientific tests on numerous items of evidence can fuel her position that Avery is innocent, while, at the same time, pointing toward someone else as the culprit, Nigro said.

"That could provide the best evidence yet that Avery and Dassey didn't do this," he said.

Nigro said he's troubled by the narrative that Calumet and Manitowoc county deputies put forth a minimal effort to explore other possible suspects at the time of Halbach's disappearance, including her romantic acquaintances. Investigators also chose to disregard evidence that someone deleted several voicemail messages from Halbach's cellphone prior to her being reported missing on Nov. 3, 2005.

Nigro said he hopes that Zellner is also aggressively investigating suspicions of police misconduct and falsified evidence surrounding Avery's arrest and conviction. After all, Avery was embroiled in a $36 million wrongful conviction lawsuit against ex-Manitowoc County Sheriff Tom Kocourek after spending 18 years imprisoned for a wrongful rape conviction from 1985.

Nigro said the Wisconsin authorities only had "circumstantial evidence" pointing to Avery as a prime suspect.

"The idea that they would not have pursued other people is mind-boggling to me," Nigro said. "The idea you couldn't get details and check out the alibis, that's just shocking."

Regardless, Zellner won't have a cake walk in trying to win Avery's exoneration by unmasking a murderer at large, Nigro said.

"It's going to be challenging because I can't believe what's happened through the history of this case," Nigro said. "I think the starting point on a post-conviction appeal ... the defense is going to face an uphill battle. I would hope with the number of bizarre things that happened in this case, it certainly appears to be a miscarriage of justice here. I look at it and don't understand how Avery was convicted and also Brendan Dassey. That makes zero sense. Brendan Dassey's confession, that's just one of the biggest travesties of justice I've ever seen."

John Ferak of USA TODAY NETWORK-Wisconsin: 920-993-7115 or jferak@gannett.com; on Twitter @johnferak