Hundreds of classified documents released by the Federal Bureau of Investigation (FBI) reveal that the agency closed about six months ago the investigation into suspicions that three Saudi citizens who were in the U.S. on a diplomatic mission assisted two of the terrorists involved in the 9/11 terrorist attacks.

The FBI investigation, dubbed "Operation Encore," focused on three Saudi citizens - diplomats Fahad al-Tumiri and Musad al-Jarrah, and Omar al-Bayumi, who is suspected of serving as a Saudi intelligence agent. The suspicion was that the three provided two of the terrorists - Nawaf al-Hazmi and Khaled al-Midhar - with assistance in day-to-day activities, including the purchase of a place to live and assistance in assimilation in Southern California."

On September 11, exactly on the twentieth anniversary of the terrorist attack, a classified document was revealed stating that a Saudi citizen who had previously worked at a consulate in Los Angeles told detectives that Saudi personalities had assisted the two terrorists. However, the document revealed that the testimony did not provide unequivocal determinations regarding the active involvement of the diplomats in preparing for the attacks.

According to hundreds of new documents released in the past day on President Joe Biden's directive, the comprehensive investigation did not present enough evidence to allow an indictment against the three Saudis. The investigation files were also re-examined during 2019 and 2020 in order to "identify clues and opportunities that were missed or to investigate actions that might have advanced the investigation" and even conducted new interviews, but at the end of May this year it was decided to close the investigation.

"Nearly twenty years after the attack, the FBI has not identified any groups or individuals responsible for the attack other than those charged so far in accordance with the final conclusion of the September 11 commission of inquiry," the document said in a statement announcing the end of the investigation. However, the agency and the federal prosecution agreed that the investigation would be reopened if new significant information was discovered.

Agents also noted that in al-Qaeda, compartmentalization was maintained around the roles in carrying out the organization's major terrorist attacks and that the plans "were not communicated to others in advance for fear of leakage." "In the context of the 9/11 attacks, the hijackers knew it was a suicide mission, but they did not know what the nature of the operation was until shortly before the attack due to operational and security reasons," the memo said.