Officials have arrested two men aboard a Chicago-to-Amsterdam United Airlines flight, after it touched down in the Netherlands. The suspects, Ahmed Mohamed Nasser al Soofi and Hezem al Murisi—U.S. residents of Yemeni descent—were charged with “preparation of a terrorist attack” and arrested “at the request of American authorities,” according to a spokesman for a Dutch public prosecutor. The nature of the items al Soofi and al Murisi attempted to smuggle onboard—including a cellphone taped to a Pepto-Bismol bottle, several watches taped together, a box cutter, three large knives, and an empty shampoo bottle—led officials to believe that the pair was testing airport security in preparation for a future terrorist plot. Al Soofi made his way through airport security screenings in Birmingham, Alabama, despite officials finding $7,000 in cash and various banned items in his luggage. He then boarded a flight to Chicago’s O’Hare Airport, where he checked his luggage on a flight to Washington’s Dulles International, with connections to Dubai and Yemen. Yet Al Soofi did not board that flight. When officials learned of the rogue checked luggage, they ordered the plane back to the gate so the bag could be removed.