The assassination of John F. Kennedy in 1963 shook the nation — and spawned questions and conspiracy theories that have lingered through the decades.

Now, a group of documents released online from the National Archives will allow the public to gain a firsthand look into the investigation.

The vast majority of the 3,810 documents are FBI and CIA records. The release includes 441 documents previously fully withheld and 3,369 documents previously released with portions redacted. (In some cases, only the newly unredacted pages are being released.)

The Archives also released 17 audio files of interviews with Yuri Nosenko, a KGB officer who defected to the United States in January 1964. Nosenko claimed to have been the officer in charge of the KGB file on the man who would later assassinate Kennedy, Lee Harvey Oswald (photo below), when Oswald went to the Soviet Union in September 1959.

Separate interviews, translated from Russian and transcribed into hundreds of pages of text, reveal an agency deeply skeptical of Nosenko.

“Nosenko came forward to essentially clear the Soviet Union of any involvement in the assassination,’’ said Philip Shenon, a historian and author of “A Cruel and Shocking Act: The Secret History of the Kennedy Assassination.’’

“A lot of people at the time thought he might not be telling the truth,’’ Shenon said.

Questions of Nosenko’s credibility were settled long ago when the FBI exonerated the former KGB agent, Shenon said. The bigger mystery still surrounding the Kennedy assassination — and potentially solved by the release of these documents, he said — concerns a trip to Mexico City that Oswald took just before the assassination.

“Nobody has really ever gotten to the bottom of what went on there,’’ Shenon said.

At least a few of the newly released documents discuss the trip. But fully answering decades-old questions will take some time, Shenon said.

Monday’s release of documents is the first of several expected releases under the John F. Kennedy Assassination Records Act of 1992, which called for all records of the assassination in the Archives to be publicly disclosed after 25 years.

The sheer volume of documents to be released before October makes it challenging to search through for what Shenon called “interesting or potentially explosive information.’’

The Archives set up the John F. Kennedy Assassination Records Collection in November 1992. It includes approximately 5 million pages of records. Eighty-eight percent of the collection has already been publicly available since the late 1990s, according to the Archives.

The records-release law, enacted in response to a thirst from the public for transparency about the investigation, set up five categories of information that could be withheld from release and a board to review whether agencies were justified in postponing the release of records.

Sara Salinas can be reached at sara.salinas@globe.com. Follow her on Twitter @saracsalinas.