Investigators have searched the former property of “BTK killer” Dennis Rader, the murderer who was convicted of killing 10 people in Kansas in a bloody spree from the 1970s to 90s, as the search for connections to unsolved cases continues.

Deputies from Osage County, Oklahoma, were in Park City, Kansas, Tuesday searching a property Rader once owned. He remains incarcerated in Kansas following his 2005 sentence to 10 consecutive life terms.

“Our investigation has led to additional unsolved murders and missing persons that are possibly connected to BTK,” Osage County Undersheriff Gary Upston told NBC News Wednesday.