Police are probing a possible break in the case of missing Iowa college student Mollie Tibbetts. A red shirt found Thursday near a previously searched hog farm may belong to the missing 20-year-old. It's the first major potential clue discovered in the search for Tibbetts, who hasn't been seen since July 18 when she left her boyfriend's home to go for a run. A person mowing the lawn in the area found shirt. Investigators are now scouring ditches near the hog farm for any sign of Tibbetts.