Without a doubt at least one shot came from the grassy knoll.
The History Channel did a 6 hour series on this a few years back. Very interesting. It is titled "The Men Who Killed Kennedy". It was avaiable for purchase on their website a few years ago.
Also interesting was a book written by the brother of Sam Giancana, the Chicago mob boss. In the book, he relates a converation with Sam, where Sam alludes to his role in the assasination.
There are several valid reasons for Giancana wanting Kennedy dead. I do not recall the title of the book, but one should be able to search for it on the internet.
Another interesting read that also brushes on the assassination is called "The Band Played On".
Give them a read and see what you think.
My difficulty in accepting the grassy knoll theory is that with the thousands of people in the area, to my knowledge not one eyewitness saw the alleged grassy knoll shooter. Remember, Dallas PD handed the investigation because at the time of Kennedy's murder there was no federal law proscribing the murder of a president. Moreover, Oswald murdered a Dallas cop. Therefore, at the time the murder occurred I don't believe Dallas PD would have covered up anything over which it had authority.
When considered in its totality, it's extremely doubtful that Oswald could have murdered Kennedy without the aid of principals to that crime.
