Thursday marks 45 years since two Jacksonville, Fla. sisters, Mylette and Annette Anderson, mysteriously disappeared.

Mylette, 6, and Lillian "Annette," 11, went missing on Aug. 1, 1974. Around 6 p.m., they were left alone at their Oceanway home while their mother, Elizabeth Anderson, and their sister, Donna, went to care for a sick relative.

Loading ...

Their father, Jack, was coming home from a day of fishing. He was supposed to be home by 6 p.m. but got delayed because of boat problems. He called around 7 p.m. and spoke to the girls. While on the phone, he heard their dog barking, but Annette assured him the dog was barking at birds in the front yard.

Still, the worried father called again at 7:20 p.m. This time, no one answered the phone.

In those 20 minutes, police believe the two girls went missing.

Credit: National Center for Missing & Exploited Children
Annette Anderson, 11 (left), and Mylette Anderson, 6, went missing in 1974 after they were briefly left home alone in Oceanway.

When Jack got home, he found the family dog locked in the back bedroom and the girls were nowhere in sight. Mylette's favorite doll -- the one she carried everywhere -- was also missing.

Neighbors told police that they saw a white car in the driveway around the time the girls went missing, but they said they didn't believe they saw anything suspicious; No one saw the girls leave.

Their sister, Donna, spoke to First Coast News last year. She recalled the day they went missing.

"Whoever went in the house would have to put the little dog up in Mommy and Dadd's bedroom because he would eat them up because he was so attached to Annette," Donna said. "So badly."

Donna believes that whoever took her sisters had some kind of plan because the family lived on a secluded, single road.

Mylette and Annette's disappearance coincides with a series of disappearances that happened in the span of three months in 1974 where a total of five young girls vanished. Two of the girls' bodies -- 12-year-olds Virginia Helm and Rebecca Greene -- were found, but no arrests were made.

Elizabeth and Jack Anderson died before ever finding out what happened to their daughters.

READ MORE >> Unsolved: Three months, five missing girls and the tumultuous summer of 1974

Loading ...

Today, the case of Mylette and Annette remains cold. The only name that was ever connected to their disappearance was serial killer Paul John Knowles. 

Knowles was also known as "The Casanova Killer." He reportedly went on a four-month killing spree across seven states in 1974 and was tied to at least 18 deaths. He claimed he killed 35 people, according to Eric W. Hickey, a criminal psychology professor at California State University.

Credit: Wikipedia
Paul John Knowles, serial killer.

Knowles claimed that he killed two girls who matched Mylette and Annette's descriptions and buried them in Commonwealth. When police searched the area, however, they wound up empty.

"I can't say that he is responsible for this," Sgt. Dan Janson, with the Jacksonville Sheriff's Office's Homicide Unit, told First Coast News last year. "I am leaning toward he is not. It is a false confession just based on some of the facts that we know about this case."

Janson said Knowles was known for embellishing the number of victims he had for shock value.

Knowles died in 1974 after he attempted to shoot a Georgia sheriff. A Georgia Bureau of Investigation agent fatally shot him as a result, according to CBS News.

Mylette would have been 51 years old today. Annette would have been 56.

If you have any information about their disappearance, call the National Center for Missing and Exploited Children at 1-800-THE-LOST or JSO at 904-630-0500.

For more cold case files, visit Project: Cold Case and be sure to follow and watch First Coast News' Unsolved series: