Tom O'Neill is an American investigative journalist best known for CHAOS: Charles Manson, the CIA, and the Secret History of the Sixties, the 2019 book he wrote with Dan Piepenbring. He has spent most of his career on the Manson murders and on Cold War intelligence programs such as the CIA's MKULTRA mind-control research. UFOs were never his beat; his place in the UAP story comes from a single account he gave in 2026 of a conversation with a congressional staffer.

A magazine writer based in Venice, California, O'Neill has written for Us, Premiere, New York, the Village Voice and Details. In 1999 Premiere gave him a three-month assignment on how the 1969 Tate–LaBianca killings had changed Hollywood. He missed the deadline and kept reporting for about two decades, building the story from Freedom of Information requests and hundreds of interviews. The project cost him a contract with Penguin Press, which sued to recover his advance after repeated missed deadlines, and he has described driving for Uber and borrowing from family to keep working.

Little, Brown published CHAOS on June 25, 2019. The book challenges prosecutor Vincent Bugliosi's "Helter Skelter" motive and examines Manson's lenient treatment by parole authorities, the possibility that his followers were informants, and the CIA-linked psychiatrist Louis Jolyon "Jolly" West, who studied Haight-Ashbury hippies in the late 1960s. O'Neill acknowledges he found no direct evidence tying West to Manson. Reviews ranged from praise in the Washington Post and the Guardian to Kirkus's complaint that the book was overlong and crowded with theories. Errol Morris adapted it as the Netflix documentary CHAOS: The Manson Murders, released on March 7, 2025.

On June 30, 2026, O'Neill testified alongside Stephen Kinzer and Elizabeth Ginexi at the House hearing on MKULTRA, "Mind Control and Accountability," held by the Oversight Committee's Task Force on the Declassification of Federal Secrets under Anna Paulina Luna. C-SPAN aired his statement that he believed Congress was never told what the program actually achieved. Five days earlier he had attended the 2026 Disclosure Forum on Capitol Hill, which he said he joined by invitation rather than as a UAP specialist.

In an August 2026 interview on Andrew Gold's Heretics podcast, O'Neill said that after the forum an unnamed senior congressional staffer, who accompanies a lawmaker into secure briefing rooms, told him that "if you knew what we knew, you wouldn't be agnostic." By O'Neill's account, the staffer described classified briefings on "recovered crafts and recovered beings" and said staff with that access had been given psychological support. Liberation Times reported the account on September 4, 2026, and it spread quickly through UAP media; the staffer remains unidentified, and no committee or government office has confirmed the claims. O'Neill has said he stayed agnostic about UFOs because his CIA and murder reporting left no room for another rabbit hole, and his reputation still rests on two decades of work reopening the Manson case.