Heather was staying with friends of her family, Dana Madden and Christopher Herbert, and babysitting their two-month-old infant in July 1999. She had been staying in their residence for about a week by July 15. She was at the apartment in the 1600 block of Yale Avenue in Richmond Heights, Missouri during the overnight hours of July 15. Madden was working the night shift for her employer and the Herbert was not at home at the time. A neighbor reported observing an unidentified man carrying a child who was Heather's age out of the apartment at approximately 2:00 a.m. that morning. The child's upper body was wrapped in a blanket. When authorities were called to the scene at 5:00 a.m., they discovered that a white comforter with a floral design was missing from the apartment along with Heather. The baby was in the apartment and crying, and there was no sign of Heather, but a small amount of blood was found inside the residence. DNA testing linked the blood to Heather. She has never been heard from again.

Authorities announced that they believed Heather was not a victim of random violence and that the attacker(s) most likely knew her family or the friends she was staying with at the time. The investigation centered on a methamphetamine ring in Missouri. Evidence of a methamphetamine manufacturing lab was found in the Madden/Herbert apartment. Investigators said that Heather may have witnessed illegal drug activity in the apartment's garage and was abducted and presumably murdered as a result. In March 2002, human remains were discovered that police thought were Heather's, but they turned out not to belong to her. Investigators say they have a suspect, but there is insufficient evidence to charge the individual with anything connected to Heather's case. The suspect has not been identified publicly.

Heather's mother, Christine Kullorn, had a verbal confrontation with Madden in April 2000, nine months after her daughter vanished. She was arrested after arguing with Madden during the latter's work shift at a local 7-11 convenience store in St. Louis. Christine believes Madden and Herbert know more about her daughter's disappearance than they are telling. Herbert has given conflicting stories about his whereabouts at the time Heather disappeared; Madden was known to be at work when she vanished. Christine has been actively involved in Heather's case since the onset of the investigation and has never been considered a suspect. She says she believes her daughter will come home safe eventually.

Foul play is suspected in Heather's disappearance. She was a student at Blow Middle School in south St. Louis, Missouri at the time of her disappearance. Her case remains unsolved.