Just after 2 p.m. on November 22, 1963, the musicians of the Boston Symphony Orchestra — already onstage at Symphony Hall for a Friday afternoon concert to be simulcast on radio station WGBH — were suddenly handed new sheet music for an unscheduled change in the program. Seconds later, BSO conductor Erich Leinsdorf walked onstage and spoke directly to the gathered audience: “Ladies and gentlemen, we have a press report over the wireless. We hope that it is unconfirmed, but we have to doubt it.”

In the moments before Leinsdorf emerged from the wings, he had pre-empted the planned program and rushed the new music to his musicians, according to an interview TIME conducted with longtime BSO librarian William Shisler. Though many in the hall had already heard that President Kennedy had been shot in Dallas an hour before the concert began, nobody knew the severity of the president’s injuries. It was up to Leinsdorf to break the news to the crowd.

“The president of the United States has been the victim of an assassination.”

The audio record of this moment, captured by WGBH’s radio microphones, is nothing short of chilling. The crowd reacted with gasps and screams, even as shocked patrons shushed one another to hear the rest of Leinsdorf’s short announcement. “We will now play the Funeral March from Beethoven’s 3rd Symphony,” he continued, as the news sank in and groans of grief rippled through the hall.

With that, the BSO began its tribute to the fallen president, and for the next 13 minutes, the audience silently absorbed Beethoven’s music, played by the orchestra with a delicacy and depth of feeling that belied the fact they were playing the piece nearly sight unseen.

The JFK assassination, like September 11 and the moon landing, stands as a “Where were you?” moment for Americans. The patrons and musicians of Symphony Hall may have been at the most emotionally wrenching — and most immediately soothing — place in the country.