Some say it was just a shot form behind. From the School Book Depository. If that is true a miracle from God happens to the motion of JFK's head.
The above is a Very good extended look at Jackie's face immediately following the Explosion at Z313. Jackie is close to being cheek-to-cheek with JFK at Z313 yet her face shows No Trace of any Blood or Brain Matter. The JFK Limo Hood had traces of blood/brain matter on it, SA Kellerman & SA Greer seated in the front seat also had blood/brain matter fall upon them, both Connally's were subjected to blood/brain matter in the middle of the Limo, the back seat in which JFK and Jackie were sitting displayed Spatter throughout it, the Limo Trunk also had traces fall upon it, and DPD Officer Hargis was spattered while riding his motorcycle only feet to Jackie's Left hand side. Yet, here we see nary a trace of blood/brain matter on the face of Jackie Kennedy. This portion of the Z Film defies logic.