Derrik Sweeney had headed to Egypt in August filled with idealism, the youthful vigor of a conservative 19-year-old and a firm belief “in American freedom,” his father said Tuesday.

But after several months in the ferment of revolutionary Egypt, the Georgetown University student had become homesick and was looking forward to returning to his family in Missouri next month.

On Tuesday morning, his father, Kevin Sweeney, turned on his computer to see his son, looking pale and shaken, in the custody of Egyptian authorities, who have accused him of hurling firebombs during riots in Cairo.

With an earnest young American caught up in the throes of a distant upheaval, the scene — in images on the Internet — was a parent’s nightmare, especially for those with children studying abroad.

Egyptian authorities had filmed and photographed Derrik Sweeney, who was studying Arabic at American University in Cairo, beside two other arrested students: Luke Gates, 21, of Bloomington, Ind., who attends Indiana University; and Gregory Porter, 19, of Glenside, Pa., who attends Drexel University in Philadelphia.

In the photograph, Sweeney and Gates appear to be holding bottles of liquid as they stand against a bare wall beside Porter.

Around his neck, Gates wears what appears to be a surgical mask like the kind many demonstrators have been wearing to protect against tear gas.

In the video, a hand reaches from off camera and pushes Porter’s chin up.

Egyptian authorities have accused the students of throwing firebombs at police. The authorities allege that the men were caught on a rooftop.

The students were scheduled to be questioned in a Cairo courthouse on Tuesday afternoon.

But the university’s counsel was unable to get into the courthouse because of security concerns, and the questioning was tabled until late Tuesday evening or Wednesday morning, said Morgan Roth, a spokeswoman for American University in Cairo.

The elder Sweeney said that he had no idea whether the firebomb accusations were true.

“If he got caught up in the whole freedom thing, I suppose he could have thrown it at the police,” Sweeney said of his son. “I could see where he’d have some disagreement with tyranny.”

Sweeney, of Jefferson City, Mo., said he learned about his son’s arrest when a relative telephoned and said he had seen the story on television Tuesday morning.

Sweeney said in a telephone interview that he believed his son was being held in a courthouse in Cairo. “I’m hoping the fact that he’s 19 years old will be a mitigating factor, and, hopefully, they put him on a plane” home, he said.

“I suspect what happened is . . . that being with a bunch of Egyptian students, he probably got caught up in something. Who knows?

“I suppose thoughts of the American revolution probably were things that probably crossed his mind. He’s a huge follower of U.S. constitutional history and the Revolutionary War.

“We have endless discussions on the events of that,” he added.

The incident prompted several local colleges to check in with their students studying in Cairo and remind them to follow directions from the U.S. Embassy.

Most of the students studying abroad in the Egyptian capital are at American University in Cairo, which is also known as AUC and not related to American University in the District.

Currently, Georgetown has seven students there, the University of Virginia has three, American University has nine and George Washington University has five.

“Cairo is huge, Egypt is vast, and this is contained to one square, Tahrir Square,” said Roth, the AUC spokeswoman. Many colleges want to know whether the incident is isolated, she said, and “to our knowledge, it is.”

Derrik Sweeney, who has three siblings, was born in Chicago and moved with his family to Los Angeles and then to Missouri. He had been a student of liberal politics in high school and had worked for Barack Obama’s 2008 presidential campaign. He went to Georgetown, where he became “a staunch Republican,” his father said.

“He’s very active to get a balanced-budget amendment to the Constitution,” he said, adding that it’s “probably his number one political priority right now.”

Sweeney said his son thought that learning Arabic would help a long-term career in law, the military and politics.

“The fact that he’s an American, and the Egyptian authorities are well aware that he’s an American . . . I’m not worried he’s going to get tortured or anything like that,” his father said.

He said that he hoped “they’ll put him on a plane and deport him. I’ve never wanted my son deported before, but right now I’d be all in favor of it.”

“He liked Egypt, but the last time we talked, he said he was kind of anxious for getting back to the states,” Sweeney said, “getting kind of homesick.”

Meanwhile, Gates’s father, George Gates, said Tuesday that he was worried about his son but did not know much about his situation.

“He’s following due process in Egypt,” he said. “It’s still pretty fluid.”

Gates said his son, too, had traveled to Egypt in August and was due back next month.

“We’ve been talking to the American University, Cairo, and the embassy there,” he said. “We’re still sitting tight.”

“He was having a good time,” Gates said of his son. “We talked to him two or three days ago. He was having fun and said everybody was really friendly.”

A woman who answered the phone at a Porter family home said, “We have no comment at this time.”