Investigators are trying to piece together how a woman passed through multiple security checkpoints at New York’s JFK International Airport this week and boarded a plane to Paris, apparently hiding in the plane’s restrooms during the flight.

According to the Transportation Security Administration, the stowaway did not have a boarding pass but completed a security screening and bypassed two identity verification and boarding status stations to board a Delta Air Lines flight.

Tuesday’s incident occurred on one of the busiest travel days of the year. According to the TSA, nearly 2.7 million passengers traveled on planes that day before the Thanksgiving holiday.

Here’s what we know:

“Comprehensive investigation” underway

According to a TSA spokesman, the stowaway was not carrying any prohibited items.

It is unclear how the person managed to bypass the boarding stations before boarding the plane.

Delta said it is cooperating with law enforcement and conducting its own investigation.

“Nothing is more important than issues of safety,” a Delta spokesman said in a statement. “Therefore, Delta is conducting a comprehensive investigation into what may have happened and will work with other aviation stakeholders and law enforcement agencies to this end.”

CNN has contacted the FBI and Customs and Border Protection for further information.

Stowaway is a US green card holder

According to an airport employee in Paris, the stowaway was a woman between the ages of 55 and 60 with a Russian passport. She will soon be sent back to the United States, the official said.

The woman was placed in a waiting area at Charles de Gaulle airport – known as ZAPI – for deportees because she does not meet the requirements to enter Europe. The woman applied for asylum in France several years ago, the official told CNN.

When asked, the source did not discuss the woman’s mental state.

If the woman is sent back to the United States, the TSA could impose a civil penalty and New York authorities could arrest her, although they are not currently involved, a federal official familiar with the investigation told CNN. The TSA is conducting its own investigation into the incident, the official noted.

Pilot made an announcement about “a serious safety issue”

New York real estate agent Rob Jackson was on the Delta flight when the stowaway was discovered and told CNN that passengers were instructed to remain seated after landing so police could board the plane.

“I didn’t actually see the person in question. “Apparently she was hiding in a bathroom at the back of the plane as we were leaving JFK,” Jackson said. “The first report to passengers that there was a problem was when we were parked at the gate and they told us all to remain seated as the French police would be boarding the plane to deal with ‘a serious security issue’ to take care of.”

Jackson recorded a video of the flight captain saying, “Guys, this is the captain, we’re just waiting for the police to get on board.” They may be here now and have told us to keep everyone on the plane until “We have taken care of the extra passenger that is on the plane.”

The flight was full and there were no additional seats for the stowaway, Jackson said.

“I heard the flight attendants talking to the pilots about it – they said this person was in a restroom and then he would walk out, go to another restroom and stay there for a long time,” he said.

CNN’s Lex Harvey and Saskya Vandoorne contributed to this report.

For more CNN news and newsletters, create an account at CNN.com