But Leinsdorf is clearly not the only one in the room who knew. The orchestra is up there, ready to play a funeral march. How did they get the music? How were they already prepared?

Some wonderful reporting from James Inverne at Time answers questions that the simulcast raises. Inverne spoke with William Shisler, the orchestra's longtime librarian, who was working that day.

As Inverne tells it, Shisler and Leinsdorf both heard the news just before the concert began. In those days before cell phones, the audience wouldn't have had any way to catch wind of it as they sat waiting for the show to begin. (Some people had heard early reports out of Dallas before they arrived at the hall, but not that Kennedy was dead.)

Leinsdorf sent a message to Shisler: Find the Marcia funebre from Beethoven's Eroica Symphony. Bring it to the stage.

“The musicians were already there on the stage, in their places and of course the hall was filled with people," Shisler told Inverne. "I had to tell each of the musicians as I was handing out the music what was going on. That was the first they knew of the death. It wasn’t an easy moment, for them or for me.”

After Shisler distributed the music, he walked out into the concert hall, staking out his usual spot on the first balcony.

As Inverne tells it:

The entrance to the library is nearby and he would sometimes slip through the balcony door to listen in during rehearsals and concerts. He was an accustomed presence there, none of the ushers would have detected anything unusual. Everything seemed normal. Only Shisler knew how different this concert was about to be. “I was – standing there,” he says, haltingly, trying to express the strangeness of the moment, “Knowing he was going to make the announcement and I was about to witness that moment. I had already had my own gasp upon hearing the news, and now I’m standing there witnessing the audience about to have the same reaction. When it came, of course Leinsdorf came out and announced to the audience and there was this huge gasp, it was very emotional.” Some people left, rushing out in grief. But most, he says, stayed as the orchestra played. Many cried. Shisler was among them. “I was brought to tears by the movement of the Beethoven. It’s such beautiful music anyway.”

“I sincerely believe that music played its part in the tragedy for all of us," Shisler added. "Afterwards of course everyone was glued to the television sets for days and days. But in that period of time when we were all there, listening to Beethoven in that concert hall, we all had to respond to this terrible tragedy for ourselves. And the music sort of soothed us, reached out to each and every individual, and helped us to process what had happened.”