Lone nut or Conspiracy?

I have been paging through the book Crossfire: The Plot that Killed Kennedy, by Jim Marrs, lately wondering if Oswald, acting alone, could pull off a stunt of that magnitude. As we all know President John F. Kennedy was shot and killed on November 22nd, 1963 with the who, the why, and how being debated ever since. Could one man have carried out the shooting without help? I was also spurred on by watching Oliver Stone’s JFK.
Many people do not believe that one man could pull off three shots in the time elapsed between the first shot and the final headshot, especially not Oswald, shooting with world class precision through a sixth story window. According to his peers in the military, Oswald was a terrible shot with a rifle. He had trouble hitting stationary targets, so how could he pull off a headshot on a person in a moving car?
There’s a ton of other information, too much to get into here, ranging from the incompetence of The Warren Commission, the rush to clean the limo before any forensic evidence could be taken, the botched autopsy, to the outright charging of U.S. government with conspiracy. The most ridiculous is the “magic bullet theory”, which states that one stray bullet could account for seven wounds in Kennedy and in Governor Connally, who was sitting in the front seat.

What do you guys think? Could Lee Harvey Oswald carry out this task on his own? Do you think the federal government secretly sanctioned the plot?