Schaefer was convicted in 1973 of killing two teenage Broward County girls. He was sentenced to two life terms but was killed in December 1995 when a fellow inmate stabbed him.
While he never admitted to any other murders, Schaefer was the prime suspect in dozens of other killings. Police found writings detailing the torture, sexual abuse, and killing of women when they raided Schaefer's house, as well as belongings of five missing or dead women, TCPalm reported.
While police are confident they know who is responsible for killing Susan, Det. Springer is looking to speak to several of her friends: Julie Hunt, Michelle Williamson, and Greg Anderson.
Springer said these people may be able to help piece together Susan's final days, or many have other details that will help them finally put her case to rest after nearly five decades.
"These three could help us find the missing piece and give her family closure," police wrote in a statement. "Anyone with information please reach out to Det. Springer or remain anonymous by calling Crime Stoppers at 1-800-458-TIPS."