Allyson was last seen at approximately 7:45 a.m. on July 27, 1998, at her mother's second-floor apartment in the 100 block of Charles Street in Strasburg, Virginia. She was with her mother, Sylena Jo Dalton, at the time. At 2:25 p.m., one of Sylena's coworkers found Sylena stabbed to death on a couch inside the residence. Allyson was missing and so were several of her baby bottles. She is presumed to have been abducted by the murderer(s). Authorities believe Sylena was killed between 9:15 and 10:30 a.m. Her neighbors stated they did not hear screams or any disturbance that morning. The murder weapon had been taken from the scene.

In 2000, Sylena's mother filed a wrongful death lawsuit against Sylena's former boyfriend, Daniel E. Pompell. Sylena's mother sought $1.5 million in damages and alleged that Pompell had murdered Sylena. The outcome of the lawsuit is unknown. Pompell has never faced criminal charges in connection with Sylena's death or Allyson's disappearance, but authorities did search his home after the murder. He has cooperated with the investigation. Sylena had named Pompell as the baby's father and was seeking child support from him at the time of her death.

Authorities made an appeal for tips about the case from the public in 2005. Allyson's whereabouts remain unknown and Sylena's homicide remains unsolved.