Sandra Kaye Butler was just 16 years old when she vanished from her apartment in Sparks, Nevada in 1978. Despite her family insisting she would never have run away without telling anyone, authorities initially classified her as a runaway and did very little to find her. It wasn't until years later that the case was reclassified as a missing persons investigation. With little evidence and a series of new detectives working the case, finding credible leads has proven difficult.The primary theory is that Sandra was a victim of serial killers Charlene and Gerald Gallego, who were active in the area around the time of her disappearance. The couple, who are responsible for the deaths of 10 known victims, including two teenage girls who went missing from the same fairgrounds a year after Sandra disappeared, were eventually arrested and convicted. Gerald died in prison, while Charlene was released and relocated under a new name.However, Sandra may have also been a possible victim of another serial killer, Royal Russell Long, who was convicted of the disappearance of a 12-year-old girl and the kidnapping of her friend. Many of his presumed victims went missing from fairgrounds, leading some to theorize he may have been involved in Sandra's disappearance.In a tragic twist of fate, online sleuths have also put forward the theory that Sandra may be a Jane Doe who died after being hit by a tractor-trailer in Florida. While the age estimate doesn't match Sandra's, there are striking similarities between the two, and detectives believe the deceased may have had family in Nevada.The case of Sandra Kaye Butler remains unsolved and classified as endangered missing. If alive, she would be 59 years old. Anyone with information regarding the case is urged to contact the Sparks Police Department.