In a new documentary, pilot Tom Mannello of United Airlines Flight 23, which was scheduled to take off on September 11, 2001, believes that his plane was intended to be part of the terrorist attack.

The documentary, TMZ Investigates: 9/11: The Fifth Plane, claims to have spent six months investigating the “suspicious and alarming activities” that took place on Flight 23. Mannello states that he learned two box cutters had been found in the first-class seat pockets of the plane parked next to Flight 23, which had a tail number one digit off.

He believes that if somebody on the ground was cooperating with the terrorists, they may have made a mistake and placed the box cutters on the wrong airplane.

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In the documentary, flight attendants on Flight 23 share their suspicions about four people in first class, including two men, a child, and a person who was dressed in a hijab, with the crew believing it was a man pretending to be a woman. They also recall a man profusely sweating in business class. The flight crew reported struggling to get fruit plates for their first-class flyers, who didn’t eat meat, igniting an argument between the passengers and the first-class attendant.

Mannello says he steered the plane toward the runway, unaware of what was unfolding in Manhattan at the time. He did not get cleared to take off, however, as air traffic control ordered all flights back to their gates for a mass evacuation. The attack killed 2,996 people, including 19 hijackers aboard four flights.

Flight 23’s crew believes that they could have suffered a similar fate. TMZ reports that 20 minutes after passengers and crew members disembarked the United flight, and the aircraft was locked, people on the ground saw two uniformed individuals running in the passenger cabin. According to the documentary, when authorities came to investigate, they discovered an opened floor hatch, which led from the cabin to the belly of the plane. Mannello believes the two people may have been searching for the box cutters discovered on the neighboring plane.

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The FBI interviewed the flight attendants later that day and took them to a lineup at the Port Authority to see if they could identify the four first class passengers whose behavior drew their suspicion. No arrests were reported. The FBI declined to comment to the media, which also reached out to United Airlines.

Former Rep. Carolyn Maloney says in the documentary that she is deeply concerned that Flight 23 could have been the fifth plane. She suggests that the Intelligence Committee and Congress should look at the intelligence reports that came out from this investigation.