Central Intelligence Agency employees murdered military scientist Frank Olson in 1953 after he raised concerns about testing chemical and biological weapons on human subjects without their consent, according to a lawsuit brought by his two sons.

Eric and Nils Olson, in a complaint filed against the U.S. yesterday in Washington, said the agency has covered up the cause of their father’s death for 59 years. Frank Olson, who the CIA admitted was given LSD a few days before his death, didn’t jump from a 13th floor window of the Statler Hotel in New York City, but rather was pushed, they claim.

“The circumstances surrounding the death mirrored those detailed in an assassination manual that, upon information and belief, the CIA had drafted that same year,” Scott Gilbert, a lawyer for the Olsons, wrote in the complaint.