CHICAGO — With airline employees and police at O'Hare International Airport working in a heightened state of alert Thursday morning, a Delta Air Lines ticket agent became suspicious of a young Egyptian man who was agitated and trying to board a flight with an invalid ticket, police said.

Within minutes, she and the Chicago police officer she called for help learned that Ahmed Abou El Ela, 21, was one of 11 missing Egyptian students wanted by immigration authorities because they failed to show up at Montana State University for a study program. The police officer, Tim Bolger, arrested El Ela, and police later turned him over to federal immigration agents for questioning. He remained in federal custody Thursday evening.

Authorities said they have no evidence that any of the missing Egyptians are linked to terrorists, and police Supt. Philip Cline said there is no reason to believe El Ela's travel plans Thursday morning had anything to do with the foiled terror plot in London.

Including El Ela and two men arrested Thursday in Maryland, six of the Egyptian students have been apprehended since they disappeared after entering the country July 29. The original group was 17 students, and six reported to Montana State on time. When the others didn't show, the university contacted the Department of Homeland Security.

About 7:30 a.m. Thursday, El Ela approached one of the Delta gate desks in O'Hare's Terminal 3 and attempted to book himself onto a flight to Bozeman, Mont., Bolger said. But his ticket was for a different day, and a flight from New York to Bozeman.

He wanted to exchange the ticket, and "was acting in a strange, erratic behavior," Bolger said.

El Ela raised his voice with airline agents and told the woman to call the university to confirm he was a student there. The woman did, but a university representative told her to immediately contact authorities, Bolger said. At that point, the woman called the officer, and he soon arrived at the gate.

By that time, El Ela, who was neatly dressed in casual clothing, was "calm and cooperative," Bolger said. "He was kind of confused, and he talked in broken English."

Bolger asked him questions, but he said El Ela would not tell him where he had been recently. Police later learned that he had apparently taken a bus from New York to Chicago, police spokeswoman Monique Bond said.