Sterne told bureau chief Gerald E. Griffin that the news was "hard to believe."
"Gerry told me there was something else that was unbelievable: There was no advance obit for the president. He was so young, no one expected him to die," said Sterne.
Caught up in the "electricity and pressure of the moment," said Sterne, it was his task to do an appraisal of the president who had "served 34 months and 3 days," he wrote.
Armed with an Associated Press biographical sketch and a few reference books, Sterne sat down at his typewriter and began a marathon of writing — with much of it drawn from his memory — that commenced at 3 p.m.
As the clock edged toward 1 a.m., Griffin approached Sterne, and said, "'There is nothing more you can add; you better stop writing,'" recalled Sterne.
It ran nine columns on the front page. In the paper's first edition, the byline of "Joseph R.L. Sterne. Washington Bureau of The Sun" had been mistakenly omitted, and was later added for subsequent editions.
"It was the longest thing I've ever written," Sterne said.
By the time he had stopped typing, Sterne had smoked four packs of cigarettes and vowed to never smoke again, he said.
Sterne, along with other reporters, was in the Capitol Rotunda when Jacqueline and Caroline Kennedy entered at 2:17 p.m. Sunday and knelt at the catafalque holding the president's casket.
It was an unbearablly emotional moment in a weekend of emotional moments, he said, with many reporters who witnessed the grief-stricken scene dissolving into tears.
"Jackie whispered to Caroline, who put her hand under the flag, and then she and her mother kissed the flag," he recalled. "At that moment, we all lost our professional aplomb."
In addition to giving up smoking that evening, Sterne never read what he wrote that emotion-packed night 50 Novembers ago.
Sterne, who joined the newspaper in 1953, went on to be editorial page editor for 25 years and retired from The Sun in 1997.
Baltimore Sun researcher Paul McCardell contributed to this article.