One theory - and the most likely one to me - is that it was carried out by the Estes-Johnson-Carter-Wallace group in conjunction with the CIA. Someone shot from the grassy knoll and hit the President from the front while someone else fired from the sixth floor of the TSBD. I believe one of the shooters was Mac Wallace, who was LBJ's hatchet-man (handled by Cliff Carter), and the other was Oswald, who was CIA. I don't know which fired from where, but I remember reading that Carter told Estes that Wallace was at the grassy knoll. Billie Sol Estes was a businessman and big-league con artist who operated in Texas in the 1950's and 60's. With the help of Senator Johnson, he knocked the Department of Agriculture dead for $21 million a year in federal subsidies on his bogus cotton allotments. Henry Marshall was asked to investigate Billie Sol in 1960, and he discovered that he was buying and selling his acres at an unusually fast rate. Marshall recommended to his superiors that regulations be significantly strengthened, and Billie Sol's operations became seriously threatened. So he had A. B. Foster write to Cliff Carter, who met with Lyndon Johnson and contacted Malcolm Wallace... In the following year, Marshall was found dead - bludgeoned on the head and shot five times with a bolt-action rifle. Ruled a suicide. After getting reports of Estes borrowing money using nonexistent fertilizer storage tanks as collateral, Billie Sol was arrested by the FBI in 1962 on fraud and conspiracy charges. Lyndon Johnson distanced himself from Billie Sol and had Mac Wallace bump off people who could connect Estes with him. However, it was only a matter of time, as he was also under investigation for giving out military contracts for bribes (Indochina, anyone?) and Johnson needed the Presidency to stay out of jail. Meanwhile, Kennedy had plenty of powerful enemies behind the scenes, from the CIA to Hoffa. So, Johnson worked with the CIA, and had Carter get Wallace to hire people for the job, including Jack Ruby, Lee Harvey Oswald, and Loy Factor - a backup shooter. The President was hit twice, the Vice President took the oath, investigations ended into Johnson and eventually into the assassination, and Oswald took the blame. I should also add that there is an equally valid theory that there was only a single shooter due to bullet trajectory, but whether there was a second shooter or not, the greater theory of the Vice President's responsibility for the assassination is plausible either way. It's possible that Wallace hired Ruby and Oswald to either have someone to take the heat after Wallace made the shots (he was a stone-cold killer when Oswald was barely in junior high and would have been a more experienced marksman), or to have Oswald make the shots while Wallace took a supporting role. That covers the basics of Johnson's involvement, anyways. Anything else can be covered by those who wish to cover it.