In truth I honestly don't know. There is enough smoke of other involvement to make wondering reasonable. However, I can accept that it was possible for Oswald to be the lone gunman. One very detailed documentary revealed that Connelly was not sitting in a regular car seat at the time but was sitting in a jump seat which, especially because he had turned to look back at the President, put him in line so that the same bullet(s) that hit Kennedy could also have hit him. And that fact, if true, dispels one of the conspiracy theories that the bullet couldn't have made a turn to hit both men.
But we don't know for sure who, if anyone, hired Oswald to do the shooting, whether the same person(s) hired Ruby to take out Oswald, the theorized LBJ involvement, the Cuban connection. It all is very interesting and likely unprovable. Or if the truth is known by anyone other than those who conspired to kill Kennedy, if such people exist, nobody is talking.
So I am okay with both theories--one shooter or the grassy knoll. And wonder if some day the whole truth will come out. But for sure JFK's head was blown to smithereens and that no doubt caused his appearance to be so awful Jackie chose to keep the casket closed.