Narrative:

Shortly after takeoff and above 10;000 feet the B flight attendant called the cockpit to inform us that a passenger had been in one of the aft lavatories through a large portion of the taxi; takeoff; and climbout phases of flight. No one is sure when the pax entered the lav. He was seen exiting the lavatory after takeoff; carrying a small bag. It was later determined; by airport police to be a computer bag. With the recent ad concerning the lavatory oxygen masks/generators and the briefing given by [the] captain the flight attendants were very concerned about the extended amount of time the passenger was in the lavatory. [The] captain instructed the flight attendants to assess the passenger; question his motives; and inspect the lavatories for signs of tampering. After having done this they reported that they were not sure about the seals on the lavatory panels and wished to have them inspected by maintenance in [destination]. After questioning the passenger they determined that he had been assigned [a] seat but had chosen to sit in [another]. At this point they were questioning his story and credibility. After having followed [the] captain's instructions the flight attendants requested that we have airport police meet the aircraft and escort [passenger] off the aircraft for further questioning. At that point [the] captain directed me to contact our dispatcher to relay what we knew at this point and to coordinate the police/maintenance response with company upon our arrival. Police did in fact meet the aircraft. They questioned [the passenger] for an extended period of time and to my knowledge; released him. At this point I am not sure why or how this occurred. We had a 'good' cabin ready light in the cockpit during our taxi checklist. After the event was resolved the 'extra' flight attendant reported to [the] captain; [they had] seen the 'lav occupied' sign illuminated prior to takeoff but thought it was one of the other flight attendants in the lav. To my knowledge; all illuminated signs were operational throughout the flight. The passenger did report that he started to exit the lav prior to takeoff but chose to sit back down on the seat when it was apparent we were taking off. When and if he unlocked the door is unclear. Somewhere along the way the passenger was able to slip into the lavatory unseen.

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Original NASA ASRS Text

Title: A passenger was observed acting in a suspicious manner in one of the lavs. Police investigated at destination and the suspect was reportedly released.

Narrative: Shortly after takeoff and above 10;000 feet the B Flight Attendant called the cockpit to inform us that a passenger had been in one of the aft lavatories through a large portion of the taxi; takeoff; and climbout phases of flight. No one is sure when the pax entered the lav. He was seen exiting the lavatory after takeoff; carrying a small bag. It was later determined; by airport police to be a computer bag. With the recent AD concerning the lavatory oxygen masks/generators and the briefing given by [the] Captain the flight attendants were very concerned about the extended amount of time the passenger was in the lavatory. [The] Captain instructed the flight attendants to assess the passenger; question his motives; and inspect the lavatories for signs of tampering. After having done this they reported that they were not sure about the seals on the lavatory panels and wished to have them inspected by maintenance in [destination]. After questioning the passenger they determined that he had been assigned [a] seat but had chosen to sit in [another]. At this point they were questioning his story and credibility. After having followed [the] Captain's instructions the flight attendants requested that we have airport police meet the aircraft and escort [passenger] off the aircraft for further questioning. At that point [the] Captain directed me to contact our Dispatcher to relay what we knew at this point and to coordinate the police/Maintenance response with Company upon our arrival. Police did in fact meet the aircraft. They questioned [the passenger] for an extended period of time and to my knowledge; released him. At this point I am not sure why or how this occurred. We had a 'good' Cabin Ready light in the cockpit during our taxi checklist. After the event was resolved the 'extra' Flight Attendant reported to [the] Captain; [they had] seen the 'lav occupied' sign illuminated prior to takeoff but thought it was one of the other flight attendants in the lav. To my knowledge; all illuminated signs were operational throughout the flight. The passenger did report that he started to exit the lav prior to takeoff but chose to sit back down on the seat when it was apparent we were taking off. When and if he unlocked the door is unclear. Somewhere along the way the passenger was able to slip into the lavatory unseen.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.