CHICAGO (WLS) -- On September 18, 1966, 21-year-old Valerie Percy, one of the Percy twins and daughter of Republican candidate for U.S. Senate Charles Percy, was attacked and murdered as she slept in the family's home in north suburban Kenilworth.
Fifty years later, with no announced suspects or arrests, law enforcement officials are fighting to keep the Percy files secret.
It was a crime that mesmerized metro Chicago and is one of the nation's most notorious cold cases. There had never been a murder in Chicagoland's richest suburb. That changed literally overnight, at 5 a.m. on Sept. 18, 1966.
Millionaire businessman and soon-to-be-U.S. Senator Charles Percy and his family were awakened by shattering glass, then muffled groaning. Percy's daughter and campaign manager Valerie had just been struck and stabbed; Percy's wife saw the killer standing over her mortally-wounded daughter. It was no robbery - the man left behind Valerie's wallet, which contained $60.
The attacker quickly ran off toward the lakeshore and whoever he was, he has never been brought to justice.
The Percy files - box loads of records, reports and photographs collected by State Police and kept at Kenilworth police headquarters, have been kept secret since 1966. Now authorities are trying to block a Freedom of Information Act request by lawyers from New York and Chicago who want to make the files public.
"What we think is probably going on here is it's not a police department that is used to having a lot of scrutiny into the work that it's done, it doesn't want to be under the microscope. This is an important part of our history, this case, and the public ought to know what was investigated," said Matt Topic, FOIA attorney.
Wednesday in Cook County court, Topic will argue that after 50 years the secret Percy files should be opened up.
Lawyers for Kenilworth have given a blanket denial of that request, stating in a court memorandum that it "will obstruct the investigation." They claim the entire file should be kept under wraps because "there is an at large perpetrator... currently under active investigation."
Suburban police will not reveal any details about that claim or a possible suspect.
"I think it's tempting to read too much into that statement. I mean, to read it you would think there's a very active investigation, there's something they're looking hard at, their evidence could disappear, there could be a tampering of the witnesses. I think that is unlikely after 50 years," said Gil Soffer, ABC7 legal analyst and former federal prosecutor.
FBI records obtained by the I-Team in 2014 revealed a prime suspect in the Percy murder: William Thoresen, III, son of a Kenilworth industrial tycoon who was described in one FBI report as "violent," a "mental case... armed and dangerous."
Thoreson had uncanny connections to the Percy murder according to a Chicago author who looked into the case.
"He had 70 tons of weapons, including everything up to Howitzers, a laundry list of weapons that he had and bayonets are in there," said Glenn Wall, author of "Sympathy Vote: A Reinvestigation of the Valerie Percy Murder."
A bayonet found in Lake Michigan three days after the murder could never be connected to Valerie Percy's stabbing death, even though footprints in the sand led from the Percy home to the beach.
Even if Thoreson did it, he died in 1970 and could hardly be considered an "at large perpetrator... currently under investigation."
"They're claiming that it is an ongoing investigation and just because it's not solved doesn't mean it's really an active and ongoing investigation. And just because somebody looks at the file from time to time doesn't mean that it's an active investigation," Topic said.
Republican Charles Percy served three terms in the U.S. Senate. He died five years ago this week. His family will soon gather in Washington for a private memorial service for him and for Valerie. Son Roger Percy told the I-Team that for 50 years their family has been touched by the concern of friends and strangers, because a killer may still be out there. He asked to express the Percys' gratefulness for such public compassion.
Tuesday night the family released a statement, saying, "For fifty years, friends and total strangers alike have expressed their concern for our family and sadness for our loss. We would like them to know how very much we have appreciated their support and their remembering Valerie."
Officials fight to keep Valerie Percy murder files secret
An ABC7 I-Team Investigation