Jack Brooks
Jack Brooks (behind Jacqueline Kennedy)
Jack Brooks was a 20th century American representative in the Congress from the state of Texas.
On 22 November 1963, in the aftermath of John F. Kennedy's assassination, he witnessed Lyndon B. Johnson being administered the Presidential Oath of Office aboard Air Force One. (TOS-R: "The Cage")
The website jfklibary.org identified this individual in the photo.