DALLAS — If the most famous film showing the killing of John Kennedy in Dallas 52 years ago is worth $16 million, then surely the second-most-famous film must be worth $10 million.

At least, that’s according to a new federal lawsuit filed by the granddaughter of the late Orville Nix, who was a General Services Administration engineer working in the Santa Fe Building on Nov. 22, 1963, when he filmed the shooting of the president from a perch near Elm and Houston streets. Gayle Nix Jackson’s lawsuit, filed Saturday in federal court, demands the U.S. government return the original film or write her a check for that estimable fortune.

The film’s not exactly lost: YouTube is filled with countless iterations of what’s known as “The Orville Nix Film,” taken with a Keystone K-810 camera. It has a cameo in Oliver Stone’s “JFK.” And a high-quality first-generation duplicate of the movie sits in the archives of the Sixth Floor Museum at Dealey Plaza, which years ago posted it to the website accompanied by a lengthy history of the home movie penned by the late Gary Mack.

In fact, Nix’s family actually turned it over to the museum in 2000 after retrieving it from the FBI’s files in the early 1990s

But Jackson, Nix’s granddaughter and author of 2014’s “Orville Nix: The Missing JFK Assassination Film,” wants the long-lost original – last believed to be in the possession of the House Select Committee on Assassinations in the late 1970s. Which is why Jackson has now added a federal lawsuit to the pile of Kennedy conspiracy literature.

“This action seeks the return of the original Nix film that would provide an opportunity for researchers and others to examine the JFK assassination and grassy knoll area to confirm the Warren Commission or HSCA findings.”

Jackson, who grew up in Oak Cliff and now lives in Justin, is suing the U.S. government and the National Archives and Records Administration to retrieve the film. And, she says, if NARA can’t find it, she wants no less than $10 million.

The suit reads: “although copies were made, the US Government had the original Nix film in its possession on at least several occasions, from the time it was handed over to the FBI in December 1963; then used by the Warren Commission for its investigation an report; and again before the House Select Committee on Assassinations, headed by G. Robert Blakey, that had last possession of it in 1978.”

“According to the Warren Commission, the Nix film is nearly as important as the Zapruder film yet the public is mainly unaware of its significance.”

The suit says that if the Zapruder film is worth $16 million, per an appraisal made in 1999, then her granddad’s is worth at least $10 million.