The Fox Mulders of the world will have to wait a little longer for the full official account of John F. Kennedy’s assassination.

President Trump ordered the National Archives not to release part of the final batch of federal documents on the 1963 slaying of his predecessor on Thursday night, citing national-security concerns. The directive ran counter to Trump’s announcement earlier this month that all remaining files would be released.

“This temporary withholding from full public disclosure is necessary to protect against harm to the military defense, intelligence operations, law enforcement, or the conduct of foreign relations that is of such gravity that it outweighs the public interest in immediate disclosure,” Trump said in a memo to federal agencies.

According to the White House, federal archivists have released 2,800 documents in full on Thursday while the remainder will be released “on a rolling basis” after security vetting. “The President has demanded unprecedented transparency from the agencies and directed them to minimize redactions without delay,” White House Press Secretary Sarah Huckabee Sanders said in a statement. “The National Archives will therefore release more records, with redactions only in the rarest of circumstances, by the deadline of April 26, 2018.”

The official account of Kennedy’s assassination in November 1963 is largely accepted by historians: that the president was slain by Lee Harvey Oswald, a disaffected former Marine who was enamored with Soviet ideology, and that Oswald had no co-conspirators. The president’s death was a watershed moment in modern American history, remembered as vividly by those who lived through it as the Japanese Empire’s raid on Pearl Harbor or the 9/11 attacks.

But that explanation—that a misguided 20-something killed the most powerful man in the world for no clear reason—never quite stuck with the American public. Skepticism toward the Warren Commission’s conclusions only deepened over the next decade as the Vietnam War and Watergate sapped faith in government institutions. Today, only one-third of Americans believe that a single gunman killed Kennedy.

Congress set a ticking clock in motion for the federal government to release all its files on the assassination in 1992 when it passed the JFK Records Act. Lawmakers set a deadline to address the public’s appetite for full disclosure after the release of Oliver Stone’s film JFK in 1991. The movie casts Kennedy’s murder as part of a larger conspiracy by Lyndon B. Johnson and American intelligence agencies to seize power. The film ends with a caption stating the government’s files on the matter wouldn’t be released until 2029.

Under the JFK Records Act, the files must instead be made public by October 26, 2017, exactly 25 years after the law went into force. The National Archives has released almost 320,000 documents either in full or with redactions since then. However, a provision allows the president to keep some documents secret if their release would endanger American national security. Transparency advocates have questioned why files about one of the most important moments in modern American history should be kept from the American people.

Historians and JFK experts are largely skeptical that any bombshells linger in the government’s remaining cache. “I’ve always thought that the release of these documents is going to be something like what happened on New Year’s Eve 2000,” author Josiah Thompson told my colleague Adrienne LaFrance earlier this month. “A great big zero of happening!” Why the remaining documents would still be secret after more than a half-century may be the greater mystery. One hypothesis is that their release could expose sources and methods used by U.S. intelligence agencies in Mexico and the Soviet Union to investigate Oswald’s movements and motives.

For Trump, the sudden reversal on Thursday night squashes a moment he had publicly hyped. “Subject to the receipt of further information, I will be allowing, as President, the long blocked and classified JFK FILES to be opened,” he wrote on Twitter earlier this month, although the deadline had been established by federal law. Another tweet sent on Wednesday built the suspense as if it were a reality-television plot twist: “The long anticipated release of the #JFKFiles will take place tomorrow,” the president wrote. “So interesting!”

Trump himself is no stranger to alternative theories about Kennedy’s assassination. During the presidential campaign last year, he latched onto a National Enquirer report to suggest Rafael Cruz, the father of then-opponent Ted Cruz, may have played a role in the president’s slaying—a suggestion not backed by evidence. The elder Cruz is a Cuban emigrant who relocated to the United States in the 1950s. His son, a Texas senator, dismissed those allegations about his father as “another garbage story in a tabloid full of garbage.” Cruz told NBC he hopes the files would reveal the claim to be “beyond ludicrous.”

The National Archive will publish the final records on its website as they are released to the public.