As if the torturous confidentiality of Area 51 isn't enough, news has now surfaced that the Department of Defense has top-secret classified documents and footage about a UFO incident.

The US Navy admitted the existence of the briefings, which involves a 2004 encounter between the USS Nimitz and unidentified aerial objects, after Vice petitioned for a public records request.

Last year, the Navy recognized for the first time that three UFO videos—one from the 2004 USS Nimitz incident and two from 2015—were actual videos of strange and unidentified flying objects.

The Navy responded to Vice’s Freedom of Information Act request, saying it had “discovered certain briefing slides that are classified TOP SECRET. A review of these materials indicates that are currently and appropriate Marked and Classified TOP SECRET under Executive Order 13526 and the Original Classification Authority has determined that release of these materials would cause exceptionally grave damage to the National Security of the United States.”

The letter continued, “We have also determined that ONI possesses a video classified SECRET that ONI is not the Original Classification Authority for.”

Watch official footage captured by a US Navy F/A-18 Super Hornet fighter aircraft, which was present at the 2004 Nimitz incident off the coast of San Diego above.

According to the outlet, a Pentagon spokesperson shared that the Navy has the video of the puzzling incident in its custody but doesn’t plan to release it. “However, I can tell you that the date of the 2004 USS Nimitz video is Nov. 14, 2004,” the spokesperson told Vice. “I can also tell you that the length of the video that’s been circulating since 2007 is the same as the length of the source video. We do not expect to release this video.”