A new memo concludes that Al Qaeda did not make the attack plans known in advance to others.
The FBI has released more than 700 pages of newly declassified documents, showing how its agents failed to connect the Saudi government to the September 11 attacks.
The new FBI memo, released on Wednesday, depicted how investigators found insufficient evidence against three Saudi nationals, including a Saudi Embassy official in Washington, to charge them with illegally supporting the hijackers.
The Saudi Embassy in Washington did not respond to a request for comment on Wednesday, but issued a statement in September calling any allegations of complicity malicious and categorically false.
The FBI noted that Al Qaeda compartmentalised the roles within its major attacks and did not make the attack plans known in advance to others for fear of word getting out.
In relation to the 9/11 attacks, the hijackers knew there was a martyrdom operation, but did not know about the nature of the operation until shortly before the attack for operational security reasons, the FBI memo stated.
The documents were the latest materials to be released under an executive order from President Joe Biden aimed at making public long-classified investigative reports related to the attacks.
A separate investigative document was released on the 20th anniversary of the attacks in September.
The records have long been sought by victims' relatives as they sue in federal court in New York to try to prove that the Saudi government was complicit, something Riyadh officials have vigorously denied.
The FBI memo closing out the investigation says the bureau has not identified additional groups or individuals responsible for the attack other than those currently charged.