Officials said Delta Flight 126 turned around more than an hour into its flight Thursday night and returned to Kennedy airport in New York, the New York Daily News said.
After 277 passengers were evacuated, the NYPD Bomb Squad searched the plane with bomb-sniffing dogs.
New York police spokesman Paul Browne said wires were protruding from two straws -- one on the toilet and one in the sink of the bathroom.
"No explosive device has been found. It was determined that these wires were not part of the plane," Browne said. "Sometimes, passengers will disconnect smoke detector devices in the bathroom to have a cigarette. That has been ruled out."
Officials questioned a female passenger who had breathing problems around the time the wires were discovered to determine whether she faked illness to create a distraction but that was ruled out.
A man who was the last to use the bathroom also was questioned and said he knew nothing about the wires.
Four air marshals were aboard the flight, the News said.
The flight, bound for Madrid, had taken off at 8:10 p.m. and returned to Kennedy about 10 p.m.