Oklahoma cops believe they may have identified a woman depicted in a decades-old sketch by Dennis Rader, the serial killer known as BTK. The revelation came with the release of three drawings of women being bound and gagged inside barns—disturbing images crafted by Rader before his arrest, according to the Osage County Sheriff Eddie Virden. The sheriff told CNN his deputies are combing through “very, very good tips” from the public after the drawings’ release, but did not share the name of the woman they may have identified—only saying she’d vanished from southeast Kansas in 1991. Rader has insisted recently that he didn’t kill anyone else outside the 10 murders he’s been convicted for, but cops’ ongoing probes suggest they believe otherwise. Virden said his department is investigating the ailing 78-year-old—who dubbed himself as the BTK killer, an abbreviation for blind, torture, kill—as possibly being behind multiple unsolved disappearances in Oklahoma, Kansas, and Missouri.