But the sons did not believe the official story. After their mother died in 1993, they had their father's body exhumed.
The medical examiner's report in 1953 had described laceration's on Olson's body. The 1994 autopsy revealed a previously undisclosed hematoma on Olson's temple.
James Starrs, the George Washington University forensic pathologist who examined the body, concluded that Olson had suffered a blow to the head before he fell from Room 1018a. He called the evidence "rankly and starkly suggestive of homicide."
A CIA manual produced in the 1950s had offered advice on killing: "The most efficient accident, in simple assassination, is a fall of 75 feet or more onto a hard surface. … It will usually be necessary to stun or drug the subject before dropping him."
The Manhattan district attorney's office opened a homicide investigation in 1996. While they were unable to bring charges, they changed the official cause of death from "suicide" to "unknown."
Journalist H.P. Albarelli Jr. spent a decade interviewing Olson's surviving former colleagues and poring over documents for his 2009 book A Terrible Mistake: The Murder of Frank Olson and the CIA's Secret Cold War Experiments.
Although Albarelli differs with the Olsons on some points — he says there is no evidence that Olson witnessed "extreme interrogations" in England, or that the CIA manual was produced before Olson's death — he says he has no doubt the scientist was murdered.
But proving it now, with all the principals dead, will be a challenge.
"Who do you bring into court? Who do you depose?" Albarelli asked. "Most of the people at the CIA, the Olson case is ancient history to them."
Scott D. Gilbert, the Washington attorney representing the Olsons, said the CIA "has yet to tell the truth on any level in connection with this case" and continues to withhold "key documents."
Gilbert said he will obtain those documents, seek testimony from Cheney and Rumsfeld and get materials from the New York investigation.
"In addition, as has been our experience in other high-profile cases, we have been contacted by a number of individuals offering to share information and relevant CIA-related experiences with us, and we are investigating those leads and potential witnesses," Gilbert said. "We believe that we have seen only the tip of the iceberg in this regard."