Dennis Lynn Rader is an American serial killer known as Wichita Kansas' "Bind Torture Kill" aka "BTK" who was convicted of 10 murders which occurred between 1974 and 1991. 

3 postcards mailed to Rader by a woman who is a personal friend.
Rader has handwritten the date received on one of the 3 postcards. His writing can be seen in the scan with the backsides of the postcards.