Mattie worked as a teacher's aide at River Hills School in Cedar Falls, Iowa. She was reported missing to the Cedar Falls Police Department on March 21, 1978. She left a frozen chicken thawing in the kitchen sink for dinner. No clothing was taken and she would not have had the assets to walk away. The day after she went missing, one of her sons found her car at Black Hawk Park in Cedar Falls. The vehicle was found locked with Zabel’s purse inside. An extensive search by Black Hawk County Sheriff’s Deputies, search dogs, divers and a National Guard helicopter turned up no trace of Mattie.