Simplify the following text for a Grade 9 native English-speaking person.
Original: Lee Harvey Oswald ( October 18 , 1939 -- November 24 , 1963 ) was an American man who , according to four government investigations , killed John F. Kennedy , the 35th President of the United States , using a firearm in Dallas , Texas , on November 22 , 1963 .
Simplified: Lee Harvey Oswald ( October 18 , 1939 â `` November 24 , 1963 ) was , according to four government investigations , the gunman sniper who assassinated U.S. President John F. Kennedy in Dallas , Texas on November 22 , 1963 .