I have read and seen quite a few theories on the shooting.
Reelz channel recently had a docudrama called JFK : The Smoking Gun. It gave me more info on a different theory.
A book printed over 20 years ago -Mortal Error - poses the theory Oswald fired 2 shots at JFK - the first hit the pavement and bits of the bullet initially hit JFK. The 2nd shot from Oswald hit JFK in the neck and hit the governor of Texas in the pres. limo. Now the book poses the 3rd shot that hit JFK was shot directly behind him from a gun ( AR-15 ) that was accidentally fired by Secret Service agent Hickey ( this is info based on ballistics / weapon ammo / and trajectory ) So an Australian detective recently wrote a book called Smoking Gun and basically helped make this docudrama - he poured over all this extra info/material/interviews / etc. that was released by the AARB - an assassination review board in the mid 90's. He realized the Secret Service went to all these lengths to cover up the shooting - by interfering at the autopsy, taking evidence / etc.
Anyway - the best theory I have read / heard of - and that is based on science and straight up detective work..