JFK's killer Lee Harvey Oswald who was shot before he could testify thus the reason behind why he did it remains a mysterys thats why so many theories surround the death of JFK. Personally i would go wth the essay question "
The assassination of JFK was the result of a conspiracy of powerful forces" There is more than enough theories to support this case rather then going against it.
Main Consipiracy theories for the assasination of JFK
-White supremacists assasinated JFK namely the KKK because of his civil rights movement support
-American arms dealers who supplied weapons for the vietnam war assasinated him because JFK was trying to end the vietnam war
-Soviet spys helped in the assasination because of the cold war and JFK's blockade on cuba aka the cuban missle crisis.
-The CIA assasinated him because of the vietnam war and many disagreements.
A whole heap of consipracy theories on the assasination of JFK:
http://en.wikipedia.org/wiki/Kennedy_assassination_theories
If anyone ever needs help in modern history please pm me i'll be glad to help, im kind of a history nerd.