A notorious Kansas serial killer currently locked up in prison for 10 murders he committed could be linked to several more unsolved cases. An Oklahoma sheriff is saying old pictures Dennis Rader took of himself could link the BTK killer to more cold cases in three different states, including Kansas.

Osage County, Oklahoma, Sheriff Eddie Virden says old Polaroids Rader took of himself recreate the positions he left his victims in, and the clues include clothing he wore in some of the photos and notes he took.

Rader is currently being investigated as a possible suspect in the missing person case of Cynthia Kinney, who was last seen at an Osage County, Oklahoma, laundromat in 1976. The new information could also link Rader to nearly a half dozen cold murder / missing persons cases in Oklahoma, Missouri and Kansas.

Rader resides at the Eldorado Correction Facility, where he is serving a minimum of 175 years.