WASHINGTON (AP) _ In the two days after a rifle's crack shattered the festive tableau of a presidential motorcade, the anatomy of the Kennedy assassination emerged. And after 30 years of investigating, it remains essentially unchanged.

Extensive probing by government commissions, private sleuths, and experts in forensics, acoustics, metallurgy and the mob have added tremendous breadth to our understanding of the case.

But that vast record tells us surprisingly little that wasn't known in the frenzied 48 hours after the crime.

To the police and FBI, Lee Harvey Oswald appeared the lone shooter. They had his gun, his bullets, his palm prints, a few eyewitnesses who actually saw him fire the shots from his sixth-floor perch, and an open-and-shut case on his killing of Dallas Patrolman J.D. Tippit later that same day.

They also knew they had a potential conspiracy case on their hands. There were persistent claims of shots coming from the grassy knoll. There were Oswald's communist ties. And there was his murder at the hands of a shady Dallas nightclub owner named Jack Ruby with links to the mob.

''It was a good shooter investigation,'' said Notre Dame law Professor G. Robert Blakey, chief counsel to the House Select Committee on Assassinations. ''Within 30 hours we knew with roughly the same degree of certainty what we know now after 30 years: Oswald shot the man; he fired three times, hit him twice. That's true beyond a reasonable doubt. The sticky question is: Alone or with someone else?''

Investigators swiftly developed the single-gunman portion of the case.

At 12:45 p.m. Dallas time, fifteen minutes after the assassination, a Dallas Police dispatcher, using information provided by eyewitness Howard Brennan, broke into Channel One with the following alert: ''At Elm and Houston, reported to be an unknown white male, approximately 30, slender build, height five feet 10 inches, 165 pounds.''

In the next 65 minutes, police found the Mannlicher-Carcano bolt-action rifle, the three spent cartridges, and Oswald's palm print on a box by the sixth-floor window of the Texas School Book Depository. At about the same point police in Dealey Plaza learned that Oswald was the only depository employee missing from the building, patrolmen were closing in on Oswald in the Texas Theater after his slaying of Tippit.

Questions about a conspiracy developed with equal speed. Seconds after the assassination, a policeman in the motorcade ran his motorcycle onto the curb and ran up the grassy knoll looking for a shooter. An hour later, in a news conference at Parkland Hospital after the announcement of Kennedy's death, Dr. Malcolm Perry said the non-fatal wound in Kennedy's throat may have been the point of entry for the bullet. The remark raised questions about whether Kennedy was shot from the front and rear simultaneously.

The research conducted over the next three decades tended to do one of two things: support the single-gunman case by disproving various conspiracy allegations; or add tantalizing detail - but no solid scenario - to those pursuing the conspiracy case.

Here are some of the key developments:

- Sept. 24, 1964: The Warren Commission releases its report arguing that Oswald acted alone. It taps extensive physical, documentary, and eyewitness evidence, but finds no clear motive for the killer.

- 1966: Publication of the first major critiques of the Warren Report. ''Whitewash'' by Harold Weisberg, ''Rush to Judgement'' by Mark Lane, and ''Inquest'' by Edward Jay Epstein challenge the theory that a single bullet went through Kennedy's neck and into Texas Gov. John Connally, and the validity of other evidence.

- 1967: Josiah Thompson publishes ''Six Seconds in Dallas'' using Zapruder film to argue JFK was shot from the front-right, not the rear.

- March 7, 1967: Jack Anderson column reveals a CIA-mob plot to kill Cuban leader Fidel Castro and raises speculation that Castro ordered Oswald, a Cuban sympathizer, to kill JFK.

- 1968: A panel appointed by Attorney General Ramsey Clark concludes JFK was shot from behind. It is first of several forensic panels that will support the original autopsy.

- 1975: A House subcommittee reports that the FBI destroyed a note from Oswald to a Dallas agent delivered weeks before the assassination, raising questions about whether the agency concealed other information.

- March 1975: Geraldo Rivera airs the Zapruder film for first time on national television. The apparent movement of president's head to the left stirs conspiracy theories.

- 1976: Dr. Louis Alvarez, a Nobel Prize-winning physicist, publishes a study explaining how a shot from the rear could account for Kennedy's head movement to the left.

- 1978: Dan Moldea publishes ''The Hoffa Wars'' the first book to lay out the theory that Teamsters boss Jimmy Hoffa recruited mobsters Carlos Marcello and Santos Trafficante to arrange the assassination.

- 1979: The House Select Committee on Assassinations supports much of Warren Report but says acoustical evidence from a dictabelt tape indicates a second gunman on the grassy knoll fired at Kennedy and missed. Its report says the mob had ''means, motive and opportunity'' to execute plot.

- Oct. 4, 1981: Oswald's body is exhumed and through dental records, confirmed to be Oswald, laying to rest theories of a double or an imposter.

- 1982: A panel of 12 scientists headed by Harvard Professor Norman Ramsey finds the acoustical evidence cited by the House select committee ''seriously flawed.'' The dictabelt contains ''cross talk'' indicating that the pulses examined by the House were not gunshots.

- February 1992: Researchers examining Dallas Police files find that ''three tramps,'' long thought to have been conspirators involved in the assassination, had been arrested and were, in fact, tramps who were sleeping in a box car at the time of the slaying.

- 1992: Frank Ragano, attorney who had represented Hoffa, says that Hoffa ordered JFK killed and that he conveyed the order to Marcello and Trafficante. Some question Ragano's veracity and accuse him of trying to pump up sales of a book.

- August 1992: The Russian newspaper Izvestia reports that the Soviet KGB never recruited Oswald to be an agent or to assassinate Kennedy during the period beginning in Oct. 1959 when Oswald lived in the Soviet Union.

- August 1993: Oswald's CIA file made public at National Archives; material provides new detail on his mental condition and violent tendencies.