The FBI says all its previously withheld files relating to the 1963 assassination of John F Kennedy have been authorised for release.
The records will be published with some redactions to protect the identities of individuals who helped investigators probing his death.
By law, all government documents related to the assassination were to be released on Thursday.
But just before the release, US president Donald Trump said he had "no choice" but to agree to requests from the CIA, FBI and other agencies to continue withholding some documents to protect national security and individual identities.
Later that night, the National Archives did put a hefty cache online. It plans to release all remaining records in the coming weeks.
"The limited redactions relate to individuals who provided information during the course of the investigation, and whose lives may be at risk if they are publicly identified," said FBI spokeswoman Susan McKee.
"Every effort is being made to lift the remaining redactions going forward as those personal safety concerns are balanced with the goal of maximum transparency."
