Date: 201909
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Flight conditions: VMC
Aircraft: B767 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Parked
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; Captain
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Anomaly: Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Security; Flight Deck / Cabin / Aircraft Event Passenger Misconduct
Detector: Person Flight Attendant
When detected: Aircraft In Service At Gate
Result: General Evacuated; General Flight Cancelled / Delayed; General Police / Security Involved
Contributing factors: Human Factors; Company Policy
Primary problem: Human Factors

Narrative: Minutes after closing our doors; preparing to push off ZZZ; FA (Flight Attendant) A called to inform us a passenger wanted off the aircraft and that the Purser would call soon. We called operations to get the jetway back for the PAX (Passenger) to deplane. FA B (Purser) called and stated the passenger wanted off due to a family emergency and he did not have a checked bag. I observed the passenger standing by door 1L for a few minutes and he was acting oddly; would not make eye contact; wearing mirrored sunglasses in a dark galley. His carryon bag seemed somewhat empty from a distance to be traveling internationally. The gate agent opened and closed 1L to remove passenger. I asked FA B what seat the deplaned pax was in to verify with operations and dispatch that the correct person was removed to get accurate final weights again. She said his name did not match his seat assignment (28F) on her app and that she thought he was positive space traveling with other passengers from another airline; but didn't know what airline.At this point there were too many unanswered questions and I was concerned about the security of the flight. I spoke with FAs B & A and they mentioned the deplaned passenger had told them differing stories about why he was getting off. I talked to the FOs (First Officers) about my concerns and they both indicated there were a lot of questions we didn't have answers for. The FO mentioned other employees could read about this incident 6 months from now; wondering why we didn't take all the abnormal indicators seriously enough to request additional answers and clarity. I called Operations on their frequency; requesting the jetway back on the aircraft and asked for the Ground Security Coordinator.The gate agent reopened door 1L and GSC (Ground Security Coordinator) X & Y - who were OUTSTANDING and very professional; indicated we had to deplane the entire aircraft if we wanted to proceed with a security sweep. I made a PA; announcing we had security issue requiring the aircraft to be re-screened which would take approximately 30-60 minutes. I also indicated that we had extra fuel on board to make up some time and we were initially planning on a 45 minute early arrival; so hopefully; we'd be only slightly behind schedule. I instructed passengers to stay near the gate since we would board immediately after the issue was resolved.I spoke with the [Flight Operations Manager]; the ZZZ CP (Chief Pilot); ICE Agents; [Police] responders and [Air Carrier] TSA (Transportation Security Administration) Liaison. My initial concerns about the deplaned passenger behavior elevated when I learned he was traveling with others and they were airline employees. I began questioning what type of screening they were subjected to prior to boarding our flight. Concern focused on how they entered the secure area; via an employee line; a modified screening procedure for their airline in another terminal or normal TSA screening. My primary concern was the deplaned passenger might have left something for the others to use as a weapon.GSC was impressive; they deserve recognition as do all the others involved for their professionalism and understanding that our concerns were legitimate. They quickly and thoroughly performed the security sweep. Once the aircraft was secured; we began boarding and all passengers were grateful we had exercised caution with the security of the aircraft. We coordinated with Dispatch for a faster flight plan; confirming the required fuel was already on board for the new flight plan.Prior to departure; we learned from the ICE Agents; the deplaned passenger was displaying abnormal behavior because he was lying to the FAs about his actual reason for deplaning. ICE Agents ran his information which came back unremarkable; but they said he'd changed his story a few times with them and the [Police] upon their arrival. Eventually; he stated he was anxious about flying; did not know what 9/11 was and would nothave got off had he known how big of a deal it would be.I questioned myself several times during this process; wondering if I was overreacting to my instinct about the deplaned passenger behavior and the laundry list of unanswered questions. Ultimately; I made the decision with the support of everyone but one person; to do the safe thing and delay the flight for a thorough security sweep for any contraband that could be used as a weapon. I had just briefed the crew of the significance of the date and to perform their duties diligently and report anything they thought was out of the ordinary. I emphasized cockpit door procedures and relayed there were no known threats to our flight; but to remain vigilant.I'd like to commend everyone in ZZZ involved; thankfully the outcome was uneventful as one would hope; although an experience I will never forget.




Synopsis: B767 Captain reported security inspected aircraft after passenger requested to be removed from aircraft prior to departure.