Within a few days of the terror attacks that killed nearly 3,000 people on Sept. 11, 2001,
FBI agents identified an important possible suspect: a middle-aged Saudi graduate student
who provided crucial help to two of the al-Qaida hijackers as they settled in San Diego early the year before.

The Saudi, Omar al-Bayoumi,
had since moved to England,
and he was arrested there at the FBI’s request.

A police search of his home and office yielded a trove of evidence that quickly deepened investigators’ suspicions about Bayoumi and his dealings with the terrorists.

But what happened to much of that evidence after it was delivered to the FBI remains a mystery.

Bayoumi was questioned and released by British police and later returned to Saudi Arabia.

For years thereafter, the FBI would insist he wasn’t really a suspect at all
— that Bayoumi had met the hijackers by chance, had helped them unwittingly and seemed nothing like a militant Islamist.

As the 25th anniversary of the 9/11 attacks is marked Friday,
questions about how the FBI handled Bayoumi’s case have only grown,
driven in part by evidence that was seized from him in 2001 but not made public for years
or even shared with field agents who sought to investigate his role.

That evidence and other FBI information, now filed in a federal lawsuit against the Saudi government by victims of the attacks,
has undercut both Bayoumi’s claims of innocence and the FBI’s profile of him as a genial, pro-American civil servant.

While he was living publicly as a student, it shows, Bayoumi worked closely with Saudi religious officials,
operated as a Saudi intelligence asset
and collaborated with several clerics who would later emerge as militant Islamists tied to al-Qaida.

https://www.propublica.org/article/fbi-911-saudi-bayoumi-investigation