"It was a mixed-up jumble of corpses piled on top of each other."

That was how a Rohingya Muslim survivor described the horrific scene of a mass grave in the Myanmar village of Gu Dar Pyin. Faces of the victims appeared mutilated, possibly with acid. The survivor said he recognized his friends only by the colors of their shorts.

AP Seoul bureau chief Foster Klug, along with photographer Manish Swarup and videojournalist Rishabh Jain, both of New Delhi, were able to find evidence of five previously unreported mass graves in the village. With interviews, video they secured from someone who had been on the scene after the killings and satellite imagery, the reporting pointed to a systematic slaughter of Rohingya Muslim civilians by the military, with help from Buddhist neighbors.

Their exclusive earns the Beat of the Week.

The story started with unconfirmed reports from human rights groups and journalists that a massacre had taken place and that there were mass graves in and around Gu Dar Pyin.

Klug tracked down displaced residents from Gu Dar Pyin scattered in three refugee camps. He conducted in-depth interviews with about 30 and returned several times to focus on a handful of survivors.

Working with a local assistant and Rohingya activists, Klug tracked down displaced residents from the village scattered through three Bangladesh refugee camps. He met about 50 of them, conducted in-depth interviews with about 30 and returned several times to focus on a handful for the story.

Some people had video of bodies they said were from the massacre, but no one had time-stamped video they'd taken themselves. The AP team then met a man who led them to another who was running a kiosk on the outskirts of one of the camps. He showed Klug his video and told the dramatic story of wrapping his memory card in plastic wrap, tying it to his thigh and taking it past several checkpoints as he fled to Bangladesh.

The accounts obtained in Klug’s two dozen interviews lined up with the contents of the video. Later, Swarup and Jain went back and re-interviewed the video source and others. For further evidence of the mass burials, the AP team obtained satellite imagery of Gu Dar Pyin from DigitalGlobe.

Myanmar has cut off access to Gu Dar Pyin, so it's unclear just how many people died, but the satellite images, along with video of homes reduced to ash, reveal a village that has been wiped out. Community leaders in the refugee camps have compiled a list of 75 dead so far, and villagers estimate the toll could be higher, based on testimony from relatives and the bodies they've seen in the graves and strewn about the area. A large number of survivors carry scars from bullet wounds, including a 3-year-old boy and his grandmother.

Myanmar experts said this was the first time the use of acid had been reported in a massacre, which they said could point to a deliberate military cover-up. The Myanmar government has threatened to sue the AP over its report. However, officials have acknowledged killing and burying “19 terrorists” in the village. The government said 17 officials went to Gu Dar Pyin to investigate and were told by villagers and community leaders that "no such things happened."

The AP report rippled around the world.

The U.N. called it "extremely troubling," saying it was "very concerned." They hope to go to the region for a three-week trip this month, if given access by the government, and plan to feature Gu Dar Pyin prominently in a report to the Human Rights Commission later this year. The U.S. State Department also said it was "deeply, deeply troubled" by the reports of mass graves.

The story captured nearly two minutes of engagement with readers. Klug also did interviews with Australian TV, Al-Jazeera and two with NPR. The video was the most-watched international video that day.

For their exclusive package that detailed previously uncovered evidence of an atrocity, Klug, Swarup and Jain share this week's $500 prize.