The United States House of Representatives Select Committee on Assassinations (HSCA) was established in 1976 to investigate the John F. Kennedy assassination and the Martin Luther King, Jr. assassination. The Committee investigated until 1978, and in 1979 issued its final report, concluding that President John F. Kennedy was assassinated by Lee Harvey Oswald, probably as a result of a conspiracy. The members of this probable conspiracy were not identified. However, the committee noted that it believed that the conspiracy did not include the governments of the Soviet Union or Cuba, nor the Federal Bureau of Investigation (FBI), the Central Intelligence Agency (CIA), or the Secret Service. It also stated it did not believe the conspiracy was organized by any organized crime group, nor any anti-Castro group, but that it could not rule out individual members of any of those groups acting together.
The House Select Committee on Assassinations suffered from being conducted mostly in secret, and then issuing a public report with much of its evidence sealed for 50 years under Congressional rules. In 1992, Congress passed legislation to collect and open up all the evidence relating to Kennedy's death, and created the Assassination Records Review Board to further that goal.
The HSCA was a followup to the Hart-Schweiker and Church Committee hearings that had revealed CIA ties to other assassinations and assassination attempts. The HSCA resulted from public demands following hundreds of books, magazine articles, and video documentaries completed by private citizens and professional investigators since 1963. It was also spurred by public outcry after a copy of the Zapruder film was first shown in motion on TV in March 1975, after having been stored by Life magazine out of view of the public for almost twelve years.
On the King assassination, the Committee concluded in its report that he was killed by one rifle shot from James Earl Ray, that "there is a likelihood" that this was the result of a conspiracy, and that no U.S. government agency was part of this conspiracy probably between Earl Ray and his brothers.
The HSCA concluded in its 1979 report that:
The Committee further concluded that it was probable that:
The HSCA agreed with the single bullet theory, but concluded that it occurred at a time point during the assassination that differed from any of the several time points the Warren Commission theorized it occurred.
The Department of Justice, FBI, CIA, and the Warren Commission were all criticized for deficient job performance in their subsequent investigations, deficient in revealing to the Warren Commission information available in 1964, and the Secret Service was called deficient in their protection of the President.
In particular, the various investigations performed by the U.S. government were faulted for insufficient consideration of the possibility of a conspiracy in each case. The Committee in its report also made recommendations for legislative and administrative improvements, including making some assassinations Federal crimes.
The Chief Counsel of the Committee later changed his views that the CIA was being cooperative and forthcoming with the investigation when he learned that the CIA's special liaison to the Committee researchers, George Joannides, was actually involved with some of the organizations that Lee Harvey Oswald was involved with in the months leading up to the assassination, including an anti-Castro group, the DRE, which was linked to the CIA, where the liaison, Joannides, worked in 1963. Chief Counsel Blakey later stated that Joannides, instead, should have been interviewed by the Committee, rather than serving as a gatekeeper to the CIA's evidence and files regarding the assassination. He further disregarded and suspected all the CIA's statements and representations to the Committee, accusing it of obstruction of justice. 
The sole acoustic evidence relied on by the committee's experts to support its theory of a fourth gunshot (and a gunman on the grassy knoll) in the JFK assassination, was a Dictabelt recording alleged to be from a stuck transmitter on a police motorcycle in Dealey Plaza during the assassination. After the committee finished its work, however, an amateur researcher listened to the recording and discovered faint crosstalk of transmissions from another police radio channel known to have been made a minute after the assassination. This was supported by the National Academy of Science article.
Further, the Dallas motorcycle policeman thought to be the source of the sounds followed the motorcade to the hospital at high speed, his siren blaring, immediately after the shots were fired. Yet the recording is of a mostly idling motorcycle, eventually determined to have been at JFK's destination, the Trade Mart, miles from Dealey Plaza.
In 2001, this criticism of the Committee's acoustic evidence was rebutted in a Science and Justice article written by D.B. Thomas, a government scientist and JFK assassination researcher. He concluded the HSCA finding of a second shooter was correct and that the NAS panel's study was flawed. Thomas surmises that the Dictaphone needle jumped and created an overdub on Channel One.
"The 1981 Committee on Ballistic Acoustics was charged with reviewing the HSCA’s acoustic evidence , they concluded that the acoustic evidence of conspiracy was invalid. Donald Thomas who reportedly performed the first independent peer review of the HSCA’s work and who people think was “an expert on acoustic testing” never read Thomas ’own report on his work with the acoustic evidence in which he acknowledges that "he is not an acoustic expert" *.
In 2003, computer animator Dale Myers used various films from the day of the shooting to plot the locations and speeds of the motorcycle police officers during the assassination, and concluded that no police motorcycles were anywhere near the precise microphone location on Houston Street required by the Committee's acoustic experts. Myers' study confirmed the same misgivings voiced by HSCA photographic consultant Richard E. Sprague in 1978.
A majority of witnesses who testified on the source of the shots said they came from the direction of the Depository. However, many witnesses thought the shots came from the direction of the Knoll. Only five witnesses, from a total of over one hundred, thought the shots came from two directions simultaneously.
The Mitrokhin Archive--The KGB in Europe and the West, by Christopher Andrew and Vasili Mitrokhin, documents extensive manipulation by the KGB in creating and fostering conspiracy theories regarding the Kennedy assassination. The origin of the infamous forged letter, purported to be from Oswald to E. Howard Hunt, remained inconclusive in the final opinion of the Committee, leaving, in the words of Hunt, "an article of faith that I had some role in the Kennedy assassination."