Twelve-year-old Martha was last seen on November 27, 1985 at her family's home in Elkton, Florida by her older brother, David Allen Lambert (who was 14 years old at the time).
According to David, he last saw Martha when they were having dinner together. After dinner, she told David that she was going out and when he inquired as to where, she refused to divulge her destination.
Martha was last seen walking west on Kerri-Lynn Road in St. Augustine, Florida near her home later that night. She has never been seen again.
Martha's family life was troubled; the Lambert children had been in foster care before due to child abuse and her brothers had previously run away from home.
Martha's case was initially investigated as that of a runaway, but police eventually concluded she had not left voluntarily. Extensive searches of the area turned up no sign of her or her remains.
Authorities long suspected that David knew more about Martha's disappearance than he had disclosed. In September of 2009, David confessed to causing his sister's death. He stated they were playing on the grounds of the abandoned Florida Memorial College on King Street and Holmes Boulevard, near their home.
David and Martha got into a disagreement over money and the argument turned physical. Martha slapped David and in response, he pushed her, she fell back and hit her head on a piece of steel, which killed her.
David stated that he panicked afterwards and buried his Martha's body in a shallow grave on the grounds of the college. Investigators made considerable efforts to find Martha's body on the land where Florida Memorial College once was, but they couldn't locate any remains. They don't expect to recover Martha's body because Florida Memorial College has been razed and the area completely rebuilt.
David's statements were not made public until December 2009 and police believe his story and have closed the case. They will not file charges against him because he was a minor at the time of the incident and the statute of limitations for manslaughter has expired.
David has made many conflicting statements about his missing sister over the years; at one point, he told authorities he had heard from Martha and she was going to contact them. His 2009 confession wasn't the first time David had confessed to causing Martha's death.
When David was arrested in 2000 for passing a bad check, he told police that he was responsible for Martha's death and had buried her at a coquina mine on Holmes Boulevard. He wasn't charged at that time because investigators couldn't find Martha's body or any other evidence to support his statement.
After David's confession was publicized, his mother, Margaret Lambert Pichon, told the media that she didn't believe it, stating that David often makes up stories to get attention and thinks that others were responsible for Martha's disappearance.
Shortly after Pichon voiced her opinion, David retracted his previous statements. In media interviews he stated the police wanted to close Martha's case and he only told them what he wanted to hear. He said that he is "mentally incompetent," has long-standing emotional problems and has no idea what happened to Martha.
However, investigators still believe David was telling the truth about Martha's death and stated he became very emotional during his statement and appeared overwhelmed with grief. Cadaver dogs taken to the site where David said Martha was buried also showed a "change in behavior," although an excavation of the area turned up nothing of interest.
Martha is described as a trusting and happy person who wanted to be liked, but she had few friends at the time of her disappearance. She was a seventh-grade student at Ketterlinus Junior High School in St. Augustine, Florida in 1985.
As of 2018, Martha's case remains unsolved and foul play is suspected in Martha's case due to the circumstances involved although it remains classified as a non-family abduction or runaway with most agencies.
Martha is described as a Caucasian female with blonde hair, blue eyes, is 4'5 and weighs 70 pounds. She has birthmarks on the front of her thigh and on her upper left chest, and her upper front teeth protrude slightly.
She was last seen wearing a matching two-piece bathing suit.