This is a new case to me.. I've stumbled across many with my wanderings 
Hope folks enjoy the case!
QuoteOn December 31, 1988, Mary Fager returned home to Wichita, Kansas after visiting family for three days. When she walked in the door, she found her husband dead with two bullets in his back. In the basement, she found her nine-year-old daughter Sherri naked and strangled in the hot tub, while her 16-year-old daughter Kelli had been tied up with electrical tape and drowned.
During the ’70s and ’80s in Wichita, there was a sadistic serial killer active who had already massacred a family in 1974. He was known as the BTK killer, later to be identified as Dennis Rader. A few days after the murder, the police got a letter from BTK that said he was a fan of the murderer, but he wasn’t the one who had killed the Fagers. After Rader’s arrest in 2005, it was confirmed that Rader was indeed the one who had written the letter.
The main suspect in the case was a man named William Buttersworth. He was a contractor who had been doing renovations on the Fager’s house at the time of the murder. He was last seen December 29, 1988, and he was found on January 2 driving the Fagers’ car in Florida. He claimed that he couldn’t remember the last two days, so the judge allowed him to be put under hypnosis during the trial. In a hypnotic trance, he admitted that he had been at the Fager’s house, where he’d heard a disturbance and then seen the bodies in the house. Traumatized, he took off in the Fager’s car—to a different state. After a long trial, he was acquitted when only two jurors found him guilty. Simply put, he’d had no motive and there were no witnesses to testify against him. The case remains open to this day, with Buttersworth being the only suspect. His whereabouts are unknown.
#6 on Listverse: http://listverse.com/2014/04/29/10-haunting-unsolved-mass-murders/
A few more bits to whet your appetites for this case....
The Wichita Eagle,8/24/13: http://www.kansas.com/news/local/crime/article1121424.html
The Wichita Eagle, 11/26/12: http://www.kansas.com/news/local/crime/article1103536.html
Court transcript, State vs Butterworth, 5/25/90: http://law.justia.com/cases/kansas/supreme-court/1990/62-810-3.html
Orlando Sentinel, 1/5/88: http://articles.orlandosentinel.com/1988-01-05/news/0010040128_1_butterworth-wichita-fager
And an odd tidbit from Dennis Rader, the BTK killer.. you have to go way to the bottom of the page for the Fager family action: http://articles.orlandosentinel.com/1988-01-05/news/0010040128_1_butterworth-wichita-fager