Two men were removed from a United Airlines flight from Boston to Chicago on Tuesday morning for what passengers said was "suspicious activity."
The men, aboard early morning United Flight 636, were questioned by authorities and returned to the plane, only to be removed again after at least one passenger complained, passengers said after they arrived at O'Hare International Airport.
It was unclear whether the questioning had any connection with Monday's bombings at the Boston Marathon. The Boston Globe reported that the two passengers were later booked on a different flight.
Spokesmen for the airport, the Massachusetts State Police and the airline declined comment.
Boston Marathon finisher Matt Pomeroy, 34, and his wife Elizabeth, 33, said all seemed calm until a federal agent and a Massachusetts police officer walked onto the plane and removed two male passengers.
"The two men were taken off the plane for about 15 minutes," said Matt Pomeroy, of Johnson Creek, Wis. "They were then allowed back on but started to act suspicious."
Passenger Rich Siok, 31, of Elk Grove Village, said he didn't initially notice the two men — one of whom was in his row. To him, they looked like "average citizens."
However, Siok, who also finished the marathon Monday, said he and others began to notice the men's behavior after they were allowed back on the plane. The men, who were rows apart, began talking in a foreign language and using head and hand gestures to communicate, he said.
"It was very nerve-wracking being on the flight," Siok said. "Everyone was already nervous that they were getting back on because we didn't know what was going on."
Elizabeth Pomeroy said the two men seemed "jittery and jumpy" and were "acting suspicious."
"They were talking to each other across the rows — that doesn't normally happen," Matt Pomeroy said.
Siok said passengers around him began stirring while watching the two men communicate. As the plane approached the runway, Siok said he pressed the flight attendant call button.
"I told the flight crew, 'I don't feel comfortable with this.' And they felt the same exact way," Siok said.
At the gate, multiple FBI agents and police officers boarded the plane and escorted the two men off, Matt Pomeroy said. The passengers deplaned for another check.
Pomeroy said he and others felt safer after the additional security sweep of the plane.
"I'm glad he hit the call button — absolutely," Matt Pomeroy said. "There wasn't much communication, but I think everyone understood what was going on."
Siok said the atmosphere on the plane after the men were removed was "relieved."
"Many of the marathon runners on the plane didn't have places to be today," Siok said. "You know, it's better safe than sorry."
Jeremy Gorner and Jennifer Delgado contributed.Copyright © 2015, RedEye