Complex sentence: As soon as the shooting began, Hill jumped out and began running to overtake the moving car in front of him with the plan to climb on from the rear bumper and crawl over the trunk to the back seat where the President and First Lady were located.
Split into simpler sentences: As soon as the shooting began, Hill jumped out and began running to overtake the moving car in front of him. He climbed from the rear bumper, crawling over the trunk to the back seat where the President and First Lady were located.