Heckel was last seen leaving her office at the International Paper Company in Lock Haven, Pennsylvania on July 15, 1991. She was employed with the company as a management secretary. Heckel called her two children just before lunch that days and said she was going to run some errands and would eat her lunch alone. At the start of her lunch break she drove her car out of the parking lot and never returned. Her relatives reported her missing the next day.

Heckel's wasn't carrying any money or personal belongings at the time of her disappearance, and her financial accounts have been used since she went missing. Her car was found near the Lock Haven Hospital at 10:30 p.m. on July 17, two days after she vanished. There was no evidence of her whereabouts at the scene.

Heckel's husband was in the National Guard and was away from home on a two-week training exercise when his wife disappeared, so he was quickly ruled out as a suspect in her case. Authorities focused on another individual, Loyd Groves, one of Heckel's coworkers. Shortly before her disappearance, Heckel told a friend she was having an affair with Groves, who was also married. Heckel allegedly said she wanted to end the relationship but Groves did not. Groves's van was seen leaving the International Paper Company at around the same time as Heckel's car. Type A human blood traces of Heckel's blood type were found on the van's carpeting, the middle seat and the interior light. Heckel's blood is type A. Police also found a box of .25 caliber ammunition, a hunting knife, a partially used roll of duct tape and two athletic bags in the van, and a .25 caliber pistol in Groves's desk inside the paper plant. He denies any knowledge of Heckel's disappearance and would not even admit they were romantically involved. Groves has never been charged in her case due to lack of evidence.

Heckel's children are now grown and live outside the area. Her case remains unsolved and foul play is suspected.