The double-edged knife and leather sheath were offered on eBay for three days with a minimum bid of $100, but, The (Cleveland) Plain Dealer said Thursday, the final selling price remained a mystery.
The unidentified seller said in the description of the item that the knife was a "one of a kind" that came from the home where Castro held three young women captive for more than a decade.
Castro was not accused of stabbing or killing anyone, so the knife was apparently not seized by police. Members of Castro's family were allowed to remove various items from the house before it was razed on Aug. 7.
Castro never returned to the home after his arrest. He was sentenced to life in prison last month as part of a plea agreement.