By Samuel Burke, CNN
Most documentaries record and preserve history – only a few change the arc of history.
In Guatemala in the early 1980s, a young American documentary filmmaker named Pamela Yates bore witness to massive crimes and atrocities at great personal risk to make her film.
This year, a quarter-century later, her footage became critical evidence used to convict a military dictator of genocide.
The Central American country had been torn apart by decades of U.S. funded civil war when General Efrain Rios Montt seized power in 1982 and launched a scorched earth campaign against the Mayans and leftist guerillas.
All of these years later, a piece of tape left on the cutting room floor of Yates' documentary, "How to Nail a Dictator," became key evidence in a genocide trial against the general.
In this piece of footage, Ríos Montt clearly claims command responsibility, which is one of the most difficult burdens to prove in a court of law.
“Our strength is in our capacity to make command decisions,” he said in front of the camera at the time. “The army is ready and able to act because if I can’t control the army, then what am I doing here?”
Earlier this month, Rios Montt was convicted of genocide in a case that has deeply polarized Guatemala.
When human rights attorney Almudena Bernabeu originally saw the film she didn’t see anything important. But Yates returned to her warehouse in the swamplands of New Jersey and searched through old pieces of the tape.
“I knew when I saw it. And I immediately called Almudena,” the filmmaker told CNN’s Christiane Amanpour about the key piece of evidence that was later used in the trial.
“It was all so new in a way, to introduce footage like this as a piece of evidence,” Bernabeu said. She believes it has now pushed the envelope for future human rights cases.
On May 20, Guatemala’s Constitutional Court threw out the conviction of General Rios Montt on charges of genocide and crimes against humanity – that decision was upheld on Tuesday.
“I think what's important to know is that, first of all, it's on historical record that Efraim Rios Montt was convicted of genocide and sentenced to 80 years in prison,” the filmmaker said. “That verdict has been vacated, but the historical memory of Guatemala will now have a different narrative as it moves forward.”
In the video above you can see Christiane Amanpour’s interview with the both the attorney and the filmmaker.
CNN’s Meredith Milstein produced this piece for television.