Tammy Zywicki in August 1992. It has been 20 years since Tammy was stabbed to death while returning to college in Iowa, and her mother, 70-year-old JoAnn Zywicki, who now lives in central Florida, has managed to get through the onslaught of birthdays, holidays and special occasions that often torment families of the murdered. What gnaws her mother is the elusiveness of whoever killed her daughter in August 1992 after her car broke down along an Illinois freeway. Tammy's body was found more than a week later hundreds of miles away in southwestern Missouri, wrapped in red blanket sealed in duct tape.

Associated Press File Photo

JoAnn Zywicki, left, and her husband, Hank, pose on July 17 with a Garfield bubble gum bank and seashells that once belonged to their daughter Tammy at their home in Ocala, Fla. Two decades after Tammy was found stabbed to death along an Illinois highway while returning to college in Iowa, the case remains unsolved.

Associated Press

Tammy Zywicki on the soccer team at Grinnell College in Grinnell, Iowa, in 1990. It has been 20 years since Tammy was stabbed to death while returning to college, and her 70-year-old mother, JoAnn Zywicki, who now lives in central Florida, has managed to get through the onslaught of birthdays, holidays and special occasions that often torment families of the murdered. The case remains unsolved.

Associated Press File Photo

Bruce Mendenhall, a southern Illinois trucker who is serving a life sentence for the 2007 killing of a young woman at a Nashville truck stop, has not been ruled out as a suspect in the 20-year-old murder of Tammy Zywicki of Illinois. Zywicki was found stabbed to death in August 1992 in southwestern Missouri, hundreds of miles from where her car broke down along an Illinois highway.

Associated Press File Photo