(CNN) -- After almost two years in captivity, Peter Theo Curtis is finally home.
The American released Sunday after being held in Syria briefly addressed a gaggle of reporters in Cambridge, Massachusetts, on Wednesday.
"I had no idea when I was in prison so much effort was being expended on my behalf," he said, explaining that he was grateful for those who tried to secure his release from Islamist militants.
"Total strangers have been coming up to me (saying), 'Hey, we're just glad you're home,' said Curtis, who was dressed in jeans, sandals and a T-shirt.
"I suddenly remember how good the American people are and what kindness they have in their hearts," he added. "I'm overwhelmed by emotion."
The 45-year-old professional writer thanked journalists for expressing such great interest in him, but he said he had to bond with his mother and he just couldn't bring himself to give an interview now. "That's all I can say to you," he said, promising to give interviews later and "help you guys do your job."
"I will respond," he said, "but I can't do it now."
He then stepped away from the cameras.
An end to a traumatic ordeal
Curtis flew Tuesday from Tel Aviv, Israel, to the United States, stopping in Newark, New Jersey, before reuniting with his mother in Boston, his family said earlier in a news release.
"I have been so touched and moved, beyond all words, by the people who have come up to me today -- strangers on the airplane, the flight attendants and, most of all, my family to say welcome home," Curtis said.
Curtis' mother Nancy, said she was "overwhelmed with relief" that he had returned.
But given the recent death of American journalist James Foley, who was beheaded by militants with ISIS, she couldn't bring herself to celebrate.
Curtis was believed to have been captured in October 2012 and held by al-Nusra Front, a rebel group with ties to al Qaeda. Al-Nusra is a different rebel group than ISIS.
"I don't think anybody's in the mood of celebration. You know, we're relieved," Curtis earlier told CNN outside her home in Cambridge, Massachusetts. "But after the events of the last week and knowing those other children of my friends are in danger, you know, I have very conflicted emotions. I've come to know the other families as well, and these kids have a lot in common."
Matt Wormser, a Vermont resident and Peter Theo Curtis' former high school roommate, said it was a "very bittersweet time" for friends and relatives of the freed hostage.
"It's been tremendously difficult for Nancy," he said.
The first person Curtis contacted after confirming that her son had been released was Foley's mother, Diane, she told "ABC World News Tonight."
"You learn to get over the panic," Nancy Curtis told CNN's Anderson Cooper. "You learn to just take each hour as it comes."
Handing over a prisoner
The United Nations said Peter Theo Curtis was handed over Sunday to U.N. peacekeepers in the Golan Heights, which is under Israeli government control, and was given a medical checkup.
State Department spokeswoman Marie Harf said Curtis was brought to Tel Aviv, for medical evaluations.
Harf said he appeared to be in good health.
Curtis made a brief call to his mother Sunday, Nancy Curtis said.
"He said, 'Mom, they're just being so nice to me. They put me in this wonderful hotel, and I'm drinking a beer, and there are women out there,' " she recalled. "Because he's been in a cellar for two years, and he hasn't seen anything, no street life or obviously no women to be seen, and so he was really excited, and he was thrilled to be in Tel Aviv and frustrated that he can't go out because the place apparently is surrounded by paparazzi."
Curtis expressed gratitude to many for helping secure her son's release, including the FBI, Secretary of State John Kerry, Massachusetts Sen. Elizabeth Warren, Atlantic Media Chairman and owner David Bradley, U.N. Ambassador Samantha Power and, especially, the government of Qatar.
"Here's this extraordinary woman, and she said, 'We are going to get Theo free,' and after we made those contacts, things moved rapidly," Curtis said of Alia Al Thani, Qatar's permanent representative to the United Nations.
Qatar recently helped arrange the exchange of Sgt. Bowe Bergdahl, the only U.S. service member held by militants in Afghanistan, for five Taliban detainees held in the U.S. military base at Guantanamo Bay, Cuba.
The United States was not involved in negotiations for Peter Theo Curtis' release but was aware of private efforts to secure the release, two U.S. law enforcement officials said.
Harf said Qatari officials "told the family very clearly that they did not pay ransom" -- something the United States government, as a policy, doesn't do when dealing with kidnappers and terrorists.
An author and journalist
Curtis is an author and freelance reporter who writes under the name Theo Padnos. He contributed articles about the Middle East to various publications, including the New Republic, The Huffington Post and the London Review of Books.
He has also published two books: "My Life Had Stood a Loaded Gun," a memoir about teaching literature to young offenders at a correctional facility in Vermont, and "Undercover Muslim: A Journey into Yemen," which investigates Islamic extremism.
He was born in Atlanta and graduated from Middlebury College in Vermont. Curtis holds a doctorate in comparative literature from the University of Massachusetts and is fluent in French and Arabic, according to a statement from his family. He also speaks German and Russian.
"He had spent six years living in the Middle East," Nancy Curtis said. "He is very interested in the culture; he is fluent in Arabic. And he sees himself as someone who can help interpret what's going on there. He's particularly good at relating to ... confused young people who are trying to give meaning to their lives. Some of them get sucked up into this world of jihad."
CNN's Marisa Marcellino and Greg Botelho contributed to this report.