Coming so soon after a Nigerian was accused of trying to blow up a plane, authorities quickly responded to an emergency call from the crew on Flight 253 from Amsterdam. Some of the 256 passengers were rattled while others apparently weren't aware of the incident.
Tim Jeronimus, 13, said he was "a bit nervous" when officers entered, and his 11-year-old sister, Emma, said she was scared.
Their mother, Jane Jeronimus, said the captain told passengers that no arrival gates were available.
"I said to my husband, 'That's not true,"' she later recalled inside the terminal at Detroit Metropolitan Airport. Airport police and border officers then entered the cabin to remove the man from the plane.
Passengers were safely evacuated, and luggage was lined up on the ground for inspection by bomb-sniffing dogs.
The passenger, also a Nigerian, was a businessman who was sick and posed no security threat, said two law enforcement officials who spoke on condition of anonymity because they were not authorized to discuss the incident.
The traveler in question had "spent a lengthy time in the restroom," FBI spokeswoman Sandra Berchtold said.
"This raised concerns so an alert was raised. ... The investigation shows that this was a non-serious incident and all is clear at this point," she said.
The passenger was released after questioning, Berchtold said. The man used the bathroom several times during the trip and refused to come out as the plane was preparing to land, said Lester Robinson, head of the Wayne County Airport Authority.
"The guy didn't want to stay in his seat," said Henna Solamaa, a traveler from Finland who was aboard the Airbus 330 on Sunday.
Passengers apparently saw no cause for concern until the man got up to go to the bathroom after crew members told passengers to stay in their seats for the last hour of the flight. Witnesses said people seemed more concerned that somebody was defying crew orders, not that the man seemed suspicious.
Tim Jeronimus said crew members banged on the bathroom door several times, and the passenger refused to get out.
The Jeronimus family was sitting near the passenger. They were returning home to Ann Arbor, Mich., from a visit with relatives in the Netherlands.
Just two days earlier, Umar Farouk Abdulmutallab, 23, attempted to destroy a plane by igniting an explosive on his body shortly before arrival in Detroit, the FBI says. Passengers pounced on him to extinguish the flames.
That scare has led to new security rules that were a factor in Sunday's incident. Passengers were told to stay in their seats and keep their laps clear for the final hour.
"Even if you're sick, you have to pay respect to what the flight crew is saying," said Robert Ficano, Wayne County chief executive.
Gregory Tucker, 42, of The Hague, Netherlands, said he didn't see or hear any disruption.
"It didn't seem particularly effective," Tucker said of the new security rules.
Hitesh Desai said he was anxious throughout the incident. "It does feel surreal that this is happening," Desai, 45, of Rochester Hills, Mich., said later.
Ed White reported from Detroit. Associated Press videographer Bill Gorman in Detroit and writer Devlin Barrett in Washington contributed to this report.