The FBI says that three passengers questioned about "suspicious activity" on a Denver-to-Detroit Frontier Flight Sunday were innocent strangers and reports of two people in a restroom were wrong.Given reports of suspicious behavior and heightened security measures on the 10th anniversary of the 9/11 terrorism attacks, authorities took the precaution of scrambling fighter jets to escort Flight 623 until it safely landed at Detroit Metropolitan Airport, the FBI said. The jetliner was parked in a remote area and a bomb squad searched the plane without finding any dangerous devices.Citing law enforcement sources, ABC News reported Sunday that the "suspicious behavior" turned out to be two people "making out" in the bathroom mid-flight.The FBI debunked that scenario on Monday."It should be noted that at no time were there ever two people in the bathroom at the same time, and at no time were the three individuals uncooperative with the flight crew," Detroit FBI Special Agent Sandra R. Berchtold said in a news release.In reality, Berchtold said, the three passengers -- two men and woman -- were strangers to one another, but happened to be sitting in the same row."One of the males, who was not feeling well, got up to use the restroom during the flight," she said. "The other male got up at approximately the same time to use the restroom. The female remained seated in her row."The trio was removed from the plane and they were very cooperative while being questioned by FBI Joint Terrorism Task Force members, Berchtold said.After also interviewing crew members and several other passengers, the FBI determined there was no threat and the three passengers were released without any charges being filed, Berchtold said.The Frontier flight wasn't the only false alarm Sunday.In another incident Sunday, a pair of fighter jets were scrambled to escort an American Airlines jet into New York's John F. Kennedy International Airport after the pilot became spooked by passengers' frequent trips to and from the restroom, ABC News reported.The precaution turned out to be unnecessary as federal air marshals aboard American Flight 34 from Los Angeles to JFK were able to resolve the situation when the passengers complied with their instructions, police officials told ABC News.The pilot then radioed that the situation was under control and the plane landed safely. Three male passengers were questioned upon arrival, but no charges were filed against them, authorities said."The FBI would like to thank the public and the airlines for remaining vigilant at all times," Berchtold said.