UPDATED at 3:45 p.m. with details from United Airlines.
ST. LOUIS • A United Airlines flight to Washington from St. Louis was delayed Sunday night when the pilot requested that the plane return to the gate in St. Louis and that all passengers be rescreened.
Rumors had blamed two men posing as air marshals for causing the security scare, but the Transportation Security Administration said Monday that no one impersonated an air marshal and that there were no security risks.
What really caused the security concern? United Airlines now says the scare was triggered by paper towels stuffed in an airplane toilet.
It was a day of heightened awareness, with several incidents playing out over a background of worries about a terror plot on the anniversary of the 9/11 attacks.
Military jets escorted two flights, one to New York City and one to Detroit, after passenger visits to bathrooms caused concern. In the end, all the passengers were cleared and released in both those incidents.
In Kansas City, a man tried to pass through security with "suspicious" items and caused an evacuation. Anthony Falco Jr., 47, is now charged with trying to bring a fake bomb on board a flight.
The flight out of St. Louis was GoJet Airlines flight 3681, operating as United Express. After finding paper towels stuffed in the toilet, the crew decided to return to the airport to have the passengers and luggage rescreened out of "an abundance of caution," according to a United spokesman.
"Unrelated to the rescreening," United Airlines spokesman Rahsaan Johnson said, "prior to departure, two customers on board chose not to fly and deplaned normally. The flight operated safely and routinely and arrived just over an hour late."
But the details of the event are still unclear.
Ron Meyer, who was on the flight, says passengers were told over the PA by a flight attendant,that the men had identified themselves as air marshals but didn't have proper credentials to back that up.
Meyer, a program officer for Young America's Foundation in Herndon, Va., started much of the internet buzz about the incident by giving an interview to a talk show host by phone from his seat on the plane.
The men did not leave voluntarily but were escorted off, Meyer said. And, he says, the pilot later told him at the baggage claim in Washington that the men had been air marshals after all.
TSA wouldn't say whether the two men who got off the plane when it returned to the gate were indeed air marshals. The TSA said it does not provide information about air marshals for security reasons.
"We did not find any security issues on this flight and FAMs (federal air marshals) were not impersonated," the agency said.
Another passenger, Luke Stinson of West Springfield, Mass., said a passenger behaved oddly and walked quickly to the back of the plane. That was shortly after the plane left the gate. A short time later, it returned to the gate for rescreening.
Stinson said someone he thought to be a TSA official told passengers once they landed in Washington that the ruckus began because two men "were possibly posing as air marshals."
Meyer said he doesn't know what to make of what happened on the flight, but says he doesn't understand why the versions from the airline and TSA don't seem to match what passengers saw and were told on the flight.
The Associated Press contributed to this report.