Not entirely true.
Except for those who stood at the intersection of Elm and Houston in Dealey Plaza, JFK was not murdered in "real time". But there are thousands of morons who claim they *saw* the assassination because they later watched the Zapruder film which was not "in real time". For them, it was a recorded event. Even then, the Zapruder film was suppressed until a decade later.
The execution of Lee Harvey Oswald happened "in real time" as it was carried out on live television by NBC as they tried to document Oswald's transfer from the city jail to the county jail.
Part of Whitman's rampage was captured on live tv in Austin as it was broadcast by the local PBS affiliate that was a block or two away from the tower. All they showed, however, were puffs from the rifle.
To be more accurate, these were the first incidents shown in the media era of such a spontaneous event.
I remember seeing the shooting of Oswald on television. We were all watching TV, as we had been glued to it since the Friday, when my father yelled, ‘He shot that man!”