IIRC (I was only 8 at the time) this was the music played during that 1968 tribute to RFK:
"Abraham, Martin and John" is a 1968 song written by Dick Holler and first recorded by Dion. It is a tribute to the memory of four assassinated Americans, all icons of social change, namely Abraham Lincoln, Martin Luther King, Jr., John F. Kennedy and Robert F. Kennedy. It was written in response to the assassinations of King and the younger Kennedy in April and June 1968.
Each of the first three verses features one of the men named in the song's title, for example:
Has anybody here, seen my old friend Abraham -
Can you tell me where he's gone?
He freed a lot of people, but it seems the good, they die young
But I just looked around and he's gone.
After a bridge, the fourth and final verse mentions Robert "Bobby" Kennedy, and ends with a description of him walking over a hill with the other three men...