I watched this and was very interesting.
However it wasnt till 20+ years after 1955 that the real cause was shown in some random photographers collection that was used to make a short moving video from all the still pictures, its only then that it become obvious what happens.
It wasnt the mercs fault, the other car was out of control and swerved into the path of the merc which then drove up the back of it and took of into the crowd.