Thanks to a friend, a few years ago I got sucked into the JFK assassination and have been following a seemingly endless supply of videos on YouTube ever since.
At this point, I've swung back to Oswald as the assassin. The NOVA JFK Cold Case documentary and Oswald 48 Hours to Live, I found particularly persuasive.
The ballistic tests done by NOVA showed that the full metal jacket bullet and it's unusual shape (i.e. more surface area for a more stable trajectory) fired from the Carcano rifle was more than capable of going through both JFK and Gov. Connelly and remain in good condition. Then there's the fracturing pattern of the X-ray of the skull which indicates a shot from the back. Also interesting was the bit about the brain on the left side of the JFK's head being intact and how that contradicts the trajectory of a shot from the Grassy Knoll.
Other things learned from YouTube:
Motive: Both Nellie Connelly and Mac Kilduff thought Oswald was actually trying to kill Connelly, not JFK, because Connelly as Secretary of the Navy, had signed Oswald's dishonorable discharge.
The backyard photos of Oswald holding the rifle and pistol:
Marina Oswald says she took the photos: