Joanne was last seen at her residence on Titus Road in Bayou George, Florida sometime during May 1976. Her husband, Gary Benner, said she left in the middle of the night and never returned. She has never been heard from again.

Gary always insisted his wife left him of her own accord, but he is the prime suspect in Joanne's disappearance. Authorities stated he behaved suspiciously after she went missing, and the couple argued constantly in their marriage. When investigators searched the Benner residence, they saw what appeared to be blood in several places of the house. Gary told police the stains were nail polish and that Joanne had flung menstrual blood at him during an argument. Some carpeting was missing from the bedroom and was later found burned in a trash can. After Joanne's disappearance, Gary asked friends to mail letters and toys to his children pretending to be Joanne. The day after Joanne was last seen, her toddler-aged daughter told her aunt she had seen her mother bleeding.

Investigators obtained blood evidence from the Benner home, as well as the burned carpet and some of Gary's guns. DNA testing was not available in 1976, so they were unable to match the blood to Joanne at that time. In 2008, authorities tried to have some of the evidence analyzed, but it was too old and degraded.

Gary has never been charged in connection with Joanne's case, but investigators stated they believed he murdered Joanne and buried her body somewhere in the area. He now lives in Tennessee. He gave his youngest daughter up for adoption, but kept the older one. Joanne's disappearance remains unsolved.