Last month, I visited a displaced persons camp in South Sudan and met a woman who said she'd spent almost a year hiding in a swamp. She spent her days submerged, her head just above water. At night she'd emerge to search for food.

She's one of the hundreds of thousands of people who have fled their homes over the past two years to escape that country's brutal civil war. It's hard to imagine that so many people would give up their worldly goods and flee into the bush. A new report from Amnesty International helps explain why.

The report, issued Thursday, looks at one atrocity that not only claimed dozens of lives, but sowed fear in the living left behind.

Amnesty International says that in October of 2015, government soldiers rounded up more than 60 men and boys in Leer, a town in the northern Unity state, locked them in a shipping container until they suffocated, then dumped their bodies in a nearby field. They were accused of supporting the opposition rebels.

"Witnesses described to us how the men were detained. How they were forced into this container," says Lama Fakih, a crisis adviser with Amnesty International who spent two weeks last month in South Sudan investigating the massacre. Amnesty International interviewed 42 people who saw parts of the incident, she says. "Some [of the witnesses] were just outside the container and could hear the detainees banging on the sides of the container, screaming."

According to the report, soldiers opened the container to remove the bodies of some of the men who'd suffocated to death but then locked the doors again with the rest of the people inside. After 24 hours, all but one of the detainees were dead.

This incident is significant for several reasons. First, Amnesty International is calling it a war crime by the Sudanese government against its own people. Second, it occurred two months after the warring parties — the forces of South Sudanese President Salva Kiir and troops led by his former vice president, Reik Machar — signed a peace accord. An international commission charged with monitoring that cease-fire also documented reports of the shipping container killing in a confidential memo dated Dec. 18, 2015. Some details in that memo are slightly different from what Amnesty International found, but the main facts are strikingly similar.

The cease-fire commission's report said, "Between 20 and 22 October 2015 a group of Government Forces were involved in some sort of operation in Leer County, during which cattle were seized and about 50 people (reports vary between 53 and 60) were rounded up and put in a shipping container in Leer. The container is in the compound used by Government Forces as a headquarters. A large number of those people suffocated. Their bodies were taken and thrown into the bush along the Gandor road."

The "compound" where this happened was a church.

Government troops had commandeered the grounds of the Comboni Catholic Church in Leer after the clergy had fled. The soldiers were using the church grounds as a base.

"Unsubstantiated reports suggest that the few [detainees] who survived were killed," the cease-fire commission memo adds. "There are further reports that the only survivor was an eight-year-old boy."

Amnesty International heard that there was a lone boy who survived but puts his age at 12. One of the unnamed witnesses in the AI report says that when the shipping container was finally opened, there was a pile of bodies 3 feet high. "What we saw was tragic ... the container was full of people, they had fallen over one another and onto the floor," she's quoted as saying.

This massacre is being blamed on government forces, but reports from the African Union, Human Rights Watch and others say both sides in this civil war have committed crimes against humanity including raping women, castrating child soldiers, killing civilians and even allegedly forcing captives to drink human blood.

"Sadly this is one horrific experience in a long litany of violations that we have documented being perpetrated by government forces or allied militias against the civilian population," says Amnesty International's Lama Fakih about the shipping container incident. "And again the abuses we have documented took place after the signing of the peace agreement."

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