I remember within the last year, authorities in KS and OK were working with BTK's daughter on some cold case murders/disappearances during the time he was active but also during the time he is not known to be active...
Never really heard any updates though.
John Douglass who helped develop the FBI profiling program in his book about BTK hypothesized that Rader found some other outlet when the murders stopped but others think he may have continued killing, just not in the wichita area.
What kind of other outlet? Because I can tell you, nothing beats the pure sexual thrill of murder.
douglas surmised that during the dead time he had a job as an city code enforcement officer where he basically got to drive around and give people citations for ridiculous things.
I'm pretty sure that people even called in to complain that he was a jerk/creepy. Douglass thinks that he was likely casing people fantasizing etc.
Based on Douglass profile and his psychopathy, if there were murders, Douglass thinks that he would have been compelled to brag about them but who knows.