CHICAGO, Jan. 24 (UPI) -- FBI files seen by a Chicago television station point to the late son of an Illinois industrial tycoon as the prime suspect in the 1966 killing of Valerie Percy.
Percy, the 21-year-old daughter of former Republican Sen. Charles H. Percy, was fatally stabbed and beaten in her bedroom in the family's stately lakefront home Sept. 18, 1966, in the wealthy north shore suburb of Kenilworth during her father's first U.S. Senate campaign.
Charles Percy served nearly 20 years in the Senate. He died in 2011 at the age of 91.
No one ever was charged in his daughter's slaying -- once dubbed America's No. 1 murder mystery.
WLS-TV, Chicago, investigative reporters Friday said newly obtained information from FBI records and a new book on the crime name William Thoresen III as a prime suspect.
Thoresen lived just a 1 1/2 blocks from the Percy home and was described as "violent," and a "mental case ... armed and dangerous" in a report by FBI agents who investigated the crime.
Glenn Wall, a Chicago native who wrote a book about the Valerie Percy slaying, told WLS authorities believe she was killed with a serrated bayonet and Thoresen had been arrested in Chicago and Los Angeles for aggravated assault and possession of illegal weapons.
Police found a bayonet in Lake Michigan three days after the killing, but it was never connected to the crime. Footprints in sand led from the Percy home to the beach.
Thoresen was living in New York when he was finally found but refused to answer any questions from police. He was fatally shot by his wife in 1970. She said he once admitted to killing several people.
Valerie Percy would have been 70 had she lived. The case was never closed.