(NewsNation) — A new letter shows the U.S. government siding with Saudi Arabia and objecting to the unsealing of evidence related to the 9/11 attacks.

Families of those who died on 9/11 have filed a lawsuit seeking to release evidence they say shows the Saudi government was complicit in the attacks. Fifteen of the 19 hijackers involved in 9/11 were Saudi, and al-Qaida leader Osama bin Laden also had ties to the Saudi royal family. However, the country has denied any involvement in the attack that killed nearly 3,000 people.

The Department of Justice and FBI sent a letter to the judge overseeing the lawsuit between 9/11 victims and Saudi Arabia, asking him not to unseal the material the families are pushing to make public.

The letter, obtained from court filings, states that never-before-seen evidence should not be released when the agency has not had a chance to review it.

“In the FBI’s view, it is not appropriate to seek a blanket Privacy Act order unsealing a large collection of documents before the FBI has had the opportunity to review them. The materials cited in the PECs’ filings, including their 564-page averment, and the documents marked at depositions are voluminous, and they implicate a wide range of privacy interests and information of varying levels of potential relevance to the matters at issue in the pending motions,” the letter states.

“Moreover, while the majority of the redactions identified through the FBI’s review to date have been subject to the Privacy Act, the FBI has a broader law enforcement interest in avoiding wholesale public disclosure of the personally identifying information of U.S. persons who were witnesses or of investigative interest in FBI investigations.”

Attorneys representing the families of 9/11 victims and those representing the Kingdom of Saudi Arabia have been going back and forth over what evidence should remain under seal and what should be made public.

The families recently released a video they say shows a Saudi intelligence official casing the U.S. Capitol around the same time al-Qaida was determining targets for the 9/11 attacks.

They told NewsNation they were surprised to see the FBI weighing in on the Saudi government’s side of the issue.

The FBI did signal that if either side wanted something unsealed, it would be able to review the material and make a case-by-case judgment on whether it should be released.

But that doesn’t sit well with the families, who say the agency has had more than 20 years to go through the evidence and decide what must remain classified. Now, they want it all to be made public.

NewsNation has reached out to the FBI for comment.