A teenager who was one of three American college students arrested during massive protests in Cairo is an idealist who got caught up in the pro-democracy movement sweeping Egypt, his mother said Tuesday.

Derrik Sweeney, a 19-year-old Georgetown University student from Jefferson City, Mo., was arrested along with Luke Gates, a 21-year-old Indiana University student from Bloomington, Ind., and Gregory Porter, a 19 year-old Drexel University student from Glenside, Pa.

An Egyptian official said the students were arrested on the roof of a university building where they were throwing firebombs at security forces fighting with protesters near Tahrir Square. The official spoke on condition of anonymity because there was no authorization to speak to the media.

The three were studying at the American University in Cairo, and university spokeswoman Morgan Roth said they had been held by Egyptian authorities since their arrest but she did not know whether they had been formally charged. She said it wasn't unusual for American students to get "caught up" in Egyptian politics.

Sweeney's mother, Joy Sweeney, described him as a principled person who stands up for his beliefs. He attended previous protests but stopped after a demonstration where dozens were killed, she said. He had assured his family the violence wasn't near him and he was safe.

Still, Joy Sweeney said she wasn't surprised he went.

"He got caught up in the whole college-change-the-world mentality, and he believes in democracy strongly," she said.

But she also said her son was the family peacemaker when siblings fought and she couldn't see him acting violently.

"I don't believe that he would intentionally throw a bomb at anyone," she said. "I don't believe that."

Their parents said Sweeney and Gates had been in Cairo since August, studying Arabic along with other subjects.

Joy Sweeney said others attending previous demonstrations had praised her son's Arabic and appreciated that a "blond-hair, blue-eyed kid" was supporting their calls for democracy.

The wave of protests and violence across Egypt that began Saturday has left 29 dead and thrown the country's politics into chaos less than a week before landmark parliamentary elections were to begin. Tens of thousands of people filled Tahrir Square on Tuesday to intensify pressure on Egypt's military leaders to hand over power to a civilian government.

Joy Sweeney and Gates' father, Bill Gates, they have been in contact officials from the U.S. Embassy but have little information so far about their sons.

"I don't think anybody really knows what to expect," Bill Gates said.

The U.S. Department of State said it was aware of the detentions of three U.S. citizens in connection with Tahrir Square protests and was seeking access.

Sweeney interned earlier this year with Rep. Blaine Luetkemeyer, a Missouri Republican. Paul Sloca, a spokesman for Luetkemeyer, said Sweeney worked in the congressman's Washington office from February to May, answering phones, attending meetings and completing duties typically assigned to an intern. Sloca said Sweeney was a nice person and a hard-worker.

"We're just hoping that he's safe and that he's being treated fairly," Sloca said.

Porter graduated last year from La Salle College High School, a private preparatory school in suburban Philadelphia, school spokesman Christopher Carabello said.

In high school, Porter was a good student and "a really good kid" who excelled in debate and got seventh place in a national debate competition two years ago, he said.

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Associated Press writers Chris Blank in Jefferson City, Mo., Jessica Gresko in Washington and Patrick Walters in Philadelphia contributed to this report.