VanAlstine was last seen in Polk County, Iowa on the evening of March 26, 1976, when she put her four children to bed in their home in the 4300 block of northeast 29th Street. When her children woke up, VanAlstine was gone. She has never been heard from again. Although the nighttime temperatures were close to freezing, VanAlstine didn't take her coat or shoes with her. She also left behind her purse, her money and her car, with the door open and the keys in the ignition. Neighbors reported her missing on April 4.

There was a broken bottle on the floor of VanAlstine's apartment after her disappearance, as well as some bullet casings, but this may not have been significant. She was a very good sharpshooter who had been on on the rifle team at Iowa State University, and she and her first husband would practice shooting indoors, using the walls, mattresses, and piles of magazines to absorb the bullets. VanAlstine got a divorce from her first husband on January 3, 1975 and married her second on the same day, but they got divorced on January 1, 1976. After her disappearance, the police issued a warrant out for her arrest for child desertion.

Prior to her disappearance, VanAlstine had been a member of Minutemen, a right-wing paramilitary organization. The group believed Communists would take over America and they armed themselves and prepared for an anticipated counter-revolution. VanAlstine left the group not long before her disappearance and gave the police information about their stockpiles of weapons, ammunition and explosives. Her family believes she was assassinated by its members or sympathizers as a result; VanAlstine had allegedly feared for her life. There's no evidence to support this theory, however, and the Minutemen organization remains active in Iowa.

Although there's no hard evidence of foul play in VanAlstine's case, she was a devoted parent and close to her family and her disappearance is completely out of character. Investigators believe she may have been taken against her will. Foul play is suspected in her disappearance, which remains unsolved.

Some agencies give the date of VanAlstine's disappearance as April 2, 1976.