Officials said al Soofi was found to be carrying $7,000 in cash and a check of his luggage found a cell phone taped to a Pepto-Bismol bottle, three cell phones taped together and several watches taped together. Box-cutters and knives were also found. However, no explosives were found, so he was cleared to go onto Chicago O'Hare.
Once in Chicago, officials say he had checked luggage on a flight to Washington, D.C., but never boarded the plane. They say he met Hezam al Murisi, and the two got on a United Airlines flight Sunday night from Chicago to Amsterdam, despite security concerns.
When the flight landed in Amsterdam, they were detained by Dutch authorities at the request of American authorities.
When Customs and Border officials learned al Soofi was not on the flight from Dulles to Dubai, the plane was ordered to return to the gate so his luggage could be removed. Officials said additional screening found no evidence of explosives.
Al Soofi is believed to have ties to Yemen. His flight to Washington, D.C. had connections on flights to Dubai and the Yemen.
ABC News reporters Richard Esposito, Christine Brouwer and Brian Ross contributed to this report.