An investigation is underway after a woman made it onto a Delta flight without a boarding pass or photo identification. 

The woman boarded Flight 1516 headed for Atlanta at Orlando International Airport on Oct. 5, sitting in another passenger's seat. When asked for a boarding pass, the woman claimed she had thrown it away. 

"I thought maybe she had been assigned the seat by mistake," passenger Jenni Clemons told ABC News. "So she was very blunt from the very beginning. And she just said, 'I'm not moving.' And she never broke her gaze from the back of the seat in front of her even when all the authorities were speaking to her."

After 45 minutes, the woman was reportedly removed from the flight and passengers went through another security screening. The flight was delayed for three hours. 

According to the Washington Post, the Transportation Security Administration confirmed the woman had gone through the security checkpoint. It is unclear how she did without a boarding pass or ID. 

“Delta apologizes to customers of Flight 1516 for the delay after a person not ticketed for that flight was removed from the aircraft,” Delta said in a statement. “Delta is working with local law enforcement and the Transportation Security Administration on their investigation and we are conducting our own review of this as well. Safety and security is always our top priority.”