Stacy Peterson has been missing since October 2007 when the mother of two disappeared from her Bolingbrook home.
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RELATED: Stacy Peterson's sister keeps up search for missing remains
Her sister Cassandra Cales has long believed her husband Drew Peterson, a former Bolingbrook police officer, killed and disposed of her body by dumping it in the river. Her remains have never been found.
"I've basically devoted my life to searching," Cales said.
In May, Cales commissioned a sonar search team who volunteered their time to try to locate Peterson's remains in the murky water about 21 feet deep. At the time, the team couldn't tell if the bones they found were human.
Peterson hasn't been seen alive since October 28, 2007.
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Drew Peterson is a formal suspect in her disappearance. He will likely spend the rest of his life in prison for the murder of his wife Kathleen Savio. He's never been charged in regards to Stacy Peterson.
RELATED: 10 years later, Stacy Peterson's family hopes disappearance will be solved
Illinois State Police confirmed their Division of Criminal Investigation Zone 3 working "an active and ongoing criminal investigation" at the Chicago Sanitary & Ship Canal in Lockport. ISP said the FBI is assisting them in the investigation.
They declined to provide any further details to "protect the integrity of the case."
In the weeks after Peterson disappeared, Cales led searchers to look for her body in the Sanitary & Shipping Canal, and on numerous occasions she has claimed to ABC7 that sonar has located skeletal remains. But authorities have always come up empty.
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Most recently, Cales said she got video of skeletal remains she believes could be her sister's body.
"How many times do I have to hand my sister or whoever it is to them on a silver platter, and again they do nothing?" she wondered.
She said state police sent divers to that location Tuesday, but believes they again found nothing.
"I am very frustrated," Cales said. "We told him about this in May. But they waited five months to search."
Cales said she is committed to continuing the search for her sister's remains in part to prove to her children that she did not just run away, as well as to provide her with a proper burial.