WICHITA, Kan. (AP) — The Kansas Department of Corrections says it’s looking into reports that a website is selling letters from the serial killer known as BTK for up to $300 apiece.

KSNW-TV reports the letters were sent from El Dorado Correctional Facility by Dennis Rader, who is serving a life sentence for a series of killings that haunted Wichita for three decades.

Rader was arrested in February 2005 and confessed to 10 killings in the Wichita area between 1974 and 1991. He called himself BTK, which stood for “bind, torture, kill.”

The Corrections Department says it wants to make sure Rader is not requesting that anyone make money on his behalf.

The website’s owner says he’s interested in serial killers and posted several of Rader’s letters from prison for sale online.