Concealed in the Nile River reeds, mothers and their children crouched underwater, holding their breath as long as possible, as South Sudanese militias on the bank argued whether to hunt down and kill dozens of people hiding there.
One elderly man was spotted by a fighter onshore and ordered out, said Mabior Nyuon Bior, a doctor who was among the terrified civilians.
As the man hobbled out of the Nile, the militiaman shot him.
"Why did you do that?" Bior heard another fighter say.
"Because I can," came the response.
Two hours later, after the fighters had left, it was finally safe for Bior and other survivors to come out of the water. But by that time, he said, eight children had drowned in their mothers' arms.
When the fighters with the Lou Nuer tribe attacked his city of Bor in December, "friends were killing friends, just because it was another tribe," said Bior, a member of the Dinka tribe.
At first, he stayed at his post in Bor's hospital, operating on a badly wounded soldier and a woman facing complications in childbirth. But he had to flee into the bush when Lou Nuer fighters came, firing at him with machine guns as he ran. Some of the patients ran too, but he had to leave the woman and the soldier.
"I was fearing to die. The noise they made with their guns, boom-boom."
In the next five days, he repeatedly fled from Lou Nuer militias hunting down Dinkas in the bush. He saw four people shot down beside him as he ran. He said he saw the bodies of 10 civilians on a riverbank.
When the town was retaken by government forces, he walked back into Bor, where he found the hospital mortuary crammed with the dead. The patients he had risked his life to save had died, including the woman and her baby, left without milk.
"I was feeling bad," Bior said. "If not for this fighting, this woman would still be alive."
In the days after ethnic killings exploded in South Sudan in December, an estimated 10,000 people died in the fighting.
The atrocities were triggered by a political struggle in the governing Sudan People's Liberation Movement between President Salva Kiir and his rival and former deputy, Riek Machar, with both sides responsible for massacres, according to diplomats, witnesses and human rights organizations.
Now the fledgling country must grapple with how to move beyond the violence. Some fear that prosecuting those responsible, especially political leaders, will destabilize this volatile, fragile country, which won independence less than three years ago, and make it impossible to reach a peace deal. But human rights groups argue that South Sudan can't afford to bury the truth and grant amnesty to the killers without risking future ethnic violence.
Past peace deals in South Sudan have proved superficial and fragile, including one signed in May 2012 in Bor, the capital of Jonglei state. In some of those deals, ethnic militias were absorbed into the Sudan People's Liberation Army, the military wing of the ruling party, in effect papering over ethnic fissures.
Moreover, fighting continues despite a cease-fire agreement in January, and an estimated 850,000 people have fled their homes.
Those hiding in the river with Bior were Dinkas. In the capital, Juba, it was the Lou Nuers who fell under attack in December by members of South Sudan's security forces.
In Juba, a small city has sprung up at the United Nations peacekeeping base, with narrow alleys, makeshift shops, phone-charging businesses and women cooking over charcoal fires. It looks like any camp for displaced persons except for the neatly packed suitcases sitting outside some of the makeshift tents, and the suit carriers hanging inside, some belonging to members of parliament who fled to the camp.
William Mabany, a policeman who is a Lou Nuer, said he ran to the camp to avoid being killed by fellow officers in December. He shows a cellphone photograph of a mass grave full of twisted corpses of people who he says belonged to his tribe.
In one incident, government forces deliberately fired shots into a room full of Lou Nuer men being detained in a police building, killing more than 200 of them, according to a survivor, Mayang Yian.
Victims were identified by initiation scars on their faces or were questioned in the Dinka language and detained or killed if they couldn't answer, survivors say.
Bol Ngot, a university student in Juba, was hiding in a house with seven other Lou Nuer men when government soldiers ordered them into the street. He said he was beaten with a rifle butt and two of the others were killed, including his cousin.
"I saw soldiers shooting people, and when I saw it I ran away," he said. "My head was covered in blood. I thought they were going to kill me."
People want the truth about the killings, but not everyone wants reconciliation.
"No, no, no," said Vito Mario, 35, an oil technician from the Shilluk tribe. He fled last month to a camp for the displaced in Malakal after Lou Nuer fighters killed the family next door.
"They destroyed our lives. We don't want these people to live with us in Upper Nile state.... To live together — ," Mario trailed off, shaking his head doubtfully.
"They were saying they don't want us in this area. This is their land," said Okeng Robert, who lives in the same camp, describing a January attack by Lou Nuer militias.
Horrendous violence has touched so many families that it is difficult to know how the country can begin to heal the wounds.
In his January visit to a church in Bor where at least 14 Dinkas had been killed, Archbishop of Canterbury Justin Welby called for reconciliation and warned against impunity. Accompanying him was the archbishop of the Episcopal Church of the Sudan, Daniel Deng Bul, who had been appointed by Kiir in May to head a national committee on reconciliation. Deng earlier led a peace process in Jonglei state, where increasingly violent tit-for-tat massacres along tribal lines, usually over cattle theft, have been going on for years.
A diplomat in Juba, who spoke on condition of anonymity because the official wasn't authorized to speak, said that after the recent fighting, Deng, a Dinka, may not be acceptable to all South Sudanese to lead the reconciliation process.
Critics say that although the U.N., donors and international humanitarian agencies provide about a billion dollars a year for aid, they overlook the ethnic rifts, poor governance and bitter infighting in the Sudan People's Liberation Movement.
"On so many fronts, things were ticking along in a positive way at the end of last year," U.N. humanitarian coordinator Toby Lanzer said. "It's incredible how fast it spun out of control.
"I have asked myself, should we have been more focused on reconciliation?"
Bior, the doctor, said his country needs doctors. Before the recent fighting, he said, people would often call out to him in the street: "Thank you for what you do." So despite everything, he will return to Bor's hospital, because people need him.
When he remembers the patients who died and the morgue piled with bodies, "I blame politicians, all of them."
He's afraid that another superficial peace deal may leave the country vulnerable to violence. In Jonglei, where ethnic tension has long festered and different tribes will have to learn to live side by side, he worries that violence could explode again.
"The government should work hard on reconciliation. They have to go to the villages and talk to the people. If you want your people to have reconciliation, go there to the remote cattle camps and tell them this is how we should live."