Besides his anti-corruption work, Dagne advised Kiir on international relations and at times wrote government news releases.

Dagne played another less official job: He served as an embedded go-between, and source of intelligence, for the U.N. and U.S. diplomats trying to make sense of South Sudan’s decision-making and direction. At no time was that more important than in April, when South Sudan advanced north and captured the disputed Heglig oil field. Kiir later ordered his military to withdraw, an unpopular decision domestically.

Dagne was brought into the mission by Hilde Johnson, a former Norwegian minister of international development who heads the U.N. mission in South Sudan. Johnson was backed for that position by Ambassador Susan Rice, the U.S. representative at the U.N. in New York. Dagne, Johnson and Rice all developed close ties to the Sudan People’s Liberation Movement during their careers.

Johnson has referred to Dagne in conversation as a close friend and her best contact in Juba.

The public disclosure that South Sudan was missing $4 billion shocked South Sudan’s politicians, who’d spent years denying the scale of the problem.

According to a South Sudanese official who asked not to be identified for fear of retribution, Kiir didn’t consult his ministers before signing Dagne’s corruption letter. An official government investigation afterward found Dagne responsible for then leaking the letter to reporters through one of Kiir’s press officers, the South Sudanese official said.

South Sudanese Vice President Riek Machar, who’s a political rival to Kiir, has publicly disputed the $4 billion figure, and his spokesman said Dagne was responsible for picking that number.

"The $4 billion was not based on an investigation. It was an estimation," said James Gatdet, the vice president’s press secretary. "It was this guy Ted. There was no other source."

In response to emailed questions, the U.N. said it "is not familiar" with how the $4 billion figure was calculated.

Some in the South Sudanese government were also upset that Dagne, as a foreigner, held such a senior position in the president’s office.

Fearing for his safety, Dagne fled to Nairobi, Kenya, soon after the corruption letter was leaked. Kiir then passed a message to Dagne that he should remain outside South Sudan. Dagne later tried to return, but was refused entry.

McClatchy spoke with more than 10 people who are familiar with Dagne’s situation – friends as well as U.S., U.N. and African officials – none of whom were willing to speak on the record about his case because of the sensitivities around it.

Dagne’s fierce partisanship on the Sudan issue has made him a polarizing figure in Washington. His critics describe him as naive, or they say he hurt the reputation of the Congressional Research Service, whose website says its analysis is done "without bias."

"On the Africa side, there’ve been researchers, and they’ve been pretty unbiased, and then there was Ted," said a U.S. official who’s worked on Africa for years, who wasn’t authorized to speak on the record. The official described Dagne as "very smart" but as someone who "had an agenda and knew how to work the system."

Dagne’s wide circle of loyal friends praise him for his tenacious commitment to the cause.

Eric Reeves, an English literature professor who worked with Dagne closely in pro-Sudan People’s Liberation Movement advocacy, said his friend had made enemies in Washington because "he was too direct, too determined and not sufficiently bound by State Department or congressional protocol, especially on Sudan."

McClatchy interviewed Dagne in April in his Juba office – a prefab container inside the president’s open-air arid compound. Dagne vigorously denounced the international response to the ongoing border conflict between Sudan and South Sudan, which he viewed as one-sided in favor of Sudan.

Dagne said he wrote news releases on behalf of the government and was frustrated with U.S. policy on the two countries, which he said he was trying to change to be more pro-South Sudan.

Near the end of the interview, he turned pensive and gazed out his window. He spoke of the country’s corruption, the internal tribal wars, the lack of development outside Juba.

"I’m not even South Sudanese, but as someone who waited a long time to see the benefits (of independence), it is frustrating," he said.

When reached by phone last week, Dagne declined to answer any questions, saying only that he was out of the region and with his family. According to a friend, Dagne is now back in the U.S.

“What he gave up to go to South Sudan, the danger he endured, the emails I received about his life there," his friend Reeves wrote in an email. "I hope you at least understand – as Ted most certainly did – what a target he was by virtue of his role in helping root out corruption. Think of who that made his enemies! A lot of guys, with a lot of money, with a lot of followers, with a lot of guns."