In 2003, a Jordanian named Ra'ed al-Banna stood in line at Customs to enter Chicago, with the correct immigration papers and a legitimate reason to be in America.
But he was denied entry after a system the United States uses to analyse airline reservation data flagged that he deserved "a little extra scrutiny". In his conversations with Customs officers, his answers did not add up.
Two years later, he resurfaced, in bold headlines, when he drove a truck into a crowd of police recruits in Hilla, Iraq, and detonated a massive bomb that killed more than 130 people.
Top American counter-terrorism official Nathan Sales cited the incident to underline how travel data could be a powerful counter-terrorism tool. He called on South-east Asian governments to do more to collect and share travel data to better detect and halt terrorists in transit, especially with Islamic State in Iraq and Syria (ISIS) fighters returning home to the region as the group loses ground in the Middle East.
"The ISIS physical caliphate in Syria and Iraq is on its last legs, but that doesn't mean the terrorist threat is over. It simply means the threat is changing," said Mr Sales, a counter-terrorism coordinator at the State Department.
He was speaking to The Straits Times in an interview yesterday at the US Ambassador's residence, where the American flag was lowered to half-mast in memory of the victims of the 9/11 terror attacks on the US exactly 17 years ago.
Mr Sales is on a five-day trip to Singapore, Malaysia and Indonesia that ends on Friday, and his agenda includes discussing with his counterparts in the region issues such as counter-terrorism cooperation, countering violent extremism, rooting out foreign terrorist fighters, as well as aviation security.
The ISIS physical caliphate in Syria and Iraq is on its last legs, but that doesn't mean the terrorist threat is over. It simply means the threat is changing.
AMERICAN COUNTER-TERRORISM OFFICIAL NATHAN SALES
Stressing the threat ISIS fighters pose to South-east Asia, he said: "These are people who made the decision to travel great distances, at great personal expense, to lend their services to the false caliphate. While they were there, they developed weapons, maybe bombing expertise, and networks of fellow terrorists and like-minded extremists.
"When they come home, they bring all that baggage with them."
He also cited the siege of Marawi city by ISIS-linked militants in the Philippines last year and the recent suicide bombings in Surabaya, Indonesia, as stark reminders that more work is needed to confront ISIS and ISIS-inspired terrorists.
He said: "Our adversaries are not going to unilaterally disarm, they're going to continue to fight. That's why regional cooperation is vitally important to address this threat."
South-east Asia has room for improvement, he said, particularly in collecting and sharing travel data that could help track these fighters' movements in and out of war zones and ferret them out.
The desired data includes airline reservation data such as the personal information and itineraries of passengers, biometric information such as fingerprints, and lists of known or suspected terrorists.
The US has been using such data to screen for potential terrorists since 9/11, and is working with countries one on one to get them to implement such tools too, he said.
"It helps us find hidden connections between known terrorists and their unknown associations, and look for suspicious patterns of travel and identify people who might have otherwise escaped our notice," he added.
Countries are now required to collect such data and more aggressively track terrorist travel under the United Nations Security Council Resolution 2396 passed last year.
The resolution, which also encourages countries to share their lists, was spearheaded by the US and co-sponsored by 66 countries.
Said Mr Sales: "If everyone in the region is collecting and analysing airline reservation data, collecting biometrics, and developing and sharing lists of known or suspected terrorists, that would dramatically improve our ability to confront this adversary."