Diana Leone was a resident of the 3000 block of West Tecos Avenue in Las Vegas, Nevada, along with her boyfriend David Dale Morgan and their two children. Leone met Morgan in 1981 when she was 16 years old, and he was 50. Shortly thereafter, she moved into his home and began working at one of his businesses, Abacus Mini-Storage.

Their relationship was marred by a long history of domestic violence. In 1989, David was charged with Leone's attempted murder when he beat her with a pipe, causing multiple fractures. However, the charges were dropped when Leone refused to testify against him in court. David was also arrested on charges of domestic violence in May 1997 and March 1999 and child endangerment in January 1992, but all charges were eventually dropped as Leone refused to cooperate with the authorities.

Leone was last seen in Las Vegas in February 2000. She left behind all of her personal belongings, including her clothes, money, and vehicle, and David did not report her as a missing person. He claimed that Leone had run off with a man named "Tim," but Leone's family reported her disappearance to the authorities eight months later.

Leone and David's seven-year-old daughter told the authorities that she witnessed her parents arguing the night before Leone vanished. The child reported that David pushed Leone through a plate glass window inside their residence, then smashed her head into their refrigerator. It is believed that the argument centered around David's suspicions that Leone was having an affair.

After conducting a search of the couple's home, investigators discovered evidence that suggested Leone did not leave of her own accord. Blood was found inside the home and near Leone's vehicle, but it is unclear if it was identified as Leone's.

David was also involved in the disappearance of his second wife, Marie Morgan, in 1980. She disappeared under suspicious circumstances, and David claimed that she left with her boyfriend. However, Vincent disappeared soon after and David confessed to Marie's sister that he ambushed Vincent, shot him in the groin, tortured him, and shot him to death. David's sister, Deloris Morgan, claimed that she was forced to help him relocate Marie's remains and that they buried her body in a large hole along Highway 95 past Indian Springs, Nevada near mile marker 124. However, Deloris was unable to identify the site and died of natural causes in 1987.

David was arrested and charged with Vincent's murder in 2007, but the case was dropped in 2012 after Fred Hackett, who witnessed Vincent's murder and helped dispose of the body, died. Cowan, Marie, and Leone's cases remain unsolved, and David is the prime suspect in all of them. Authorities suspect that Leone did not leave on her own and left behind her daughter, whom she was very close to, as well as a teenage son. Leone's body has never been found.