The fliers focus on Michael Powell's Ford Taurus and a Ford Focus Josh Powell rented on Dec. 8, 2009. Cox hopes the fliers jog someone's memory of seeing the two cars together.
Josh Powell returned the Focus two days later with more than 800 miles on it. During those two days, he activated newly purchased cellphones in Tremonton, Cox wrote.
The same month Susan Powell disappeared, Michael Powell's 1997 Ford Taurus supposedly broke down near Pendleton and he sold it to a salvage yard in that town.
"They may have worked together and drove two different cars. ... That puts two silver cars in the same area over a short period of time," Cox said.
Police searched rural Oregon for Susan Powell's body earlier this month and searched the Taurus for evidence in September 2011, but neither proved fruitful.
They also looked for her in abandoned mine shafts and across Utah and Nevada deserts. But after 3½ years, the West Valley City Police Department announced Monday that it has closed its active investigation into her disappearance.
Still, Cox isn't going to stop.
"I believe that in some old outbuilding, abandoned shed, culvert or other structure or ditch near a road that was accessible ... we could find Susan," Cox wrote in the online post. "As her father I have to look."
He and the investigator will only have time to pass out fliers. But sometime in the future, Cox wants to return to the miles of highway and search more closely, checking out abandoned buildings or other places his daughter's body might be.
Though the case is closed, police administrators and the city manager said detectives would investigate any new leads.
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