His friends say Peter Biar Ajak is supremely intelligent, charismatic, and well-read, a scholar steeped in complex economic theory who cares deeply about his homeland.

And now he's in serious trouble.

The 2007 La Salle University graduate has been arrested in South Sudan and taken to one of that African country's most notorious prisons. He was detained by national security forces while boarding a plane in Juba, the capital, and has been held without charges for the last two to three days.

Though largely unknown in the United States, in other nations Ajak is viewed as a prominent political activist, a leader who has called for a new, peaceful generation to run South Sudan, a land convulsed by civil war, poverty, and corruption.

"We have all always said Peter will be the president of South Sudan one day," said his friend Ryan Meisser, a La Salle classmate.

It's no exaggeration to say Ajak, 34, rose from the depths to the heights, eagerly engaging every opportunity afforded to him.

He was one of the "Lost Boys," the nickname given to about  40,000 children who were displaced or orphaned during an earlier Sudanese civil war, which ended in 2005. For years, he wandered hundreds of miles, trading one refugee camp for another.

Ajak came to the U.S. in 2001, finding a home with a sponsor family in Philadelphia and largely teaching himself how to speak English.

He graduated from the city's Central High School, went to La Salle, earned a master's degree at the Harvard Kennedy School and, at the time of his arrest, was studying for a doctorate at the University of Cambridge in England. He was the first person from South Sudan to study at that school.

Now, he's in custody at the headquarters of the South Sudan National Security Service, a place known as the Blue House because of its tinted windows.

Political detainees there face starvation or death, the Associated Press reported. Amnesty International — which has called for Ajak's immediate, unconditional release — has documented cases of prisoners being tortured with knives, and beaten with belts and bamboo sticks.

"The charges and the motive for his arrest is not known," Ajak's brother, Deng Ajak, said in a statement to the Sudan Tribune. "We, the concerned family members, urged the arresting authorities to respect his rights and liberties."

Nearly 1,000 people signed a change.org petition that called for Ajak's release and was addressed to the United Nations, U.S. House of Representatives, World Bank, and others.

"He was a super-active leader on campus, beloved by a large group of us," said Aaron Spence, who graduated with Ajak in 2007. "A lot of people on campus are affected by what's happening to him."

Spence said he has been communicating with Ajak's family, who told him they were allowed to speak with him for 30 minutes. He has not been tortured or questioned, they said.

Ajak has been living in Kenya while speaking out against the South Sudanese government and working as an activist, Spence said. A wife and young son remain in Nairobi.

He is chairman of the South Sudan Young Leaders Forum, the Red Army Foundation, and NxGeneration of South Sudan. He was on his way to a meeting with other activists when he was arrested, friends said.

"We must stop thinking that the so-called leaders will bring peace to South Sudan," Ajak said in a recent Twitter post. "We, the great people of South Sudan, must organize ourselves to bring about the peace we deserve!"

South Sudan became independent from Sudan only in 2011, and remains mired in conflict.

During the last year, armed warfare has expanded and new, armed opposition groups have emerged, according to Amnesty International. Hundreds of thousands of people have been displaced by violence and hunger.

The factions fighting the civil war continue "to commit crimes under international law, and human rights violations, and abuses with impunity," the rights group said. The violence has had "a devastating humanitarian impact on the civilian population."

La Salle University tweeted that the community's thoughts and prayers are with Ajak, and people are hoping for his safe release. Friends have mounted an awareness campaign on social media under the #FreePeterBiar hashtag.

"He might be the biggest threat to established power in that country," Meisser said. "Peter is a special person. He's touched every life that he's ever met. He rubs elbows with the elite of the world, but he's still a very down-to-earth individual."

Ajak came to Philadelphia as an unaccompanied minor, taking classes to learn basic English and figure out how to navigate the city. He entered La Salle through its Academic Discovery Program, which provides support services for students who could benefit from extra academic help.

He excelled at La Salle, becoming involved in the university's newspaper and political and economic associations, according to a La Salle Magazine profile. He credited the school's Catholic values and virtues with cementing his sense of purpose.

"It made it something concrete that I could feel, something that I could connect to every single day," he said. "Being a Lost Boy taught me how cruel and tough life could be. However, at the same time, it taught me what a difference the individual could make in the larger scheme."

Ajak worked as a World Bank economist based in South Sudan, advising the government on economic policy and development, according to the International Growth Centre in London, where he was a senior adviser. He also founded South Sudan Wrestling Entertainment, a firm that uses South Sudanese indigenous wrestling to promote peace and reconciliation.

"Life is a gift, but I also believe that there's a duty to it," Ajak told La Salle Magazine. "To have access to so much opportunity means you have to be responsible for other things."