The official government investigation, The Warren Commission, found that Lee Harvey Oswald, acting on his own, was responsible for the crime. Since then, alternate theories and evidence to support those theories, have been presented showing that Oswald was part of a larger conspiracy involving a group of people working to kill the President.
This film was made by Abraham Zapruder. Those who believe in the “conspiracy” theory hold this up as proof Oswald not the only shooter (behind and above the President) but that there was also at least one other shooter to the right, and in front, of President Kennedy.
(Warning: the head shot occurs at 0:19 of the video. It’s grainy, but still gruesome.)
A 2001 Gallup Poll showed that 80% of Americans do NOT believe Oswald acted alone.