That gripping account by Schanberg and his story of his Cambodian friend and assistant Dith Pran's captivity under and survival of the Khmer Rouge reign of terror inspired the 1984 film "The Killing Fields" by director Roland Joffe.
Schanberg had suffered a massive heart attack Tuesday. He died in Poughkeepsie, New York, said his friend and former colleague at The New York Times, Charles Kaiser.
"Syd was a brilliant writer, a fearless reporter, and an important role model for me," Kaiser said in a Facebook post.
While the diplomatic community and other Western reporters fled Cambodia as the Khmer Rouge under Pol Pot approached Phnom Penh in 1975, Schanberg and Dith chose instead to stay behind.
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The Times described Schanberg as "a nearly ideal foreign correspondent: a risk-taking adventurer who distrusted officials, relied on himself in a war zone and wrote vividly of political and military tyrants and the suffering and death of their victims with the passion of an eyewitness to history."
But Dith was eventually expelled from the compound and forced to join an exodus of Cambodians into the countryside as part of the Khmer Rouge's radical, murderous social experiment: turning Cambodia into a modern-day agrarian society.
People suspected of coming from educated, prosperous backgrounds were targeted mercilessly. An estimated two million people died in the genocide, from outright murder, starvation in labor camps or disease.
After two weeks at the embassy, Schanberg and other foreigners were trucked to Thailand. There, he filed his first report on the fall of Phnom Penh and the hellish early days of life under the Khmer Rouge and its emptying of the capital city.