After 40 or so minutes of teasing hints that its makers may have hit upon a fresh approach to found-footage thrillers, “Phoenix Forgotten” indicates the genre may be having its last gasp on life support as the movie devolves into yet another threadbare patchwork of mounting hysteria, faux cinéma vérité, and shaky-cam visual clichés.

Things begin promisingly — or at least not off-puttingly — as Sophie (Florence Hartigan) sets out to make an investigative documentary about Josh (Luke Spencer Roberts), her older brother, and his buddies Ashley (Chelsea Lopez) and Mark (Justin Mattews), who disappeared 20 years earlier while making their own film about UFO sightings. The real-life inspiration for this fiction: On March 13, 1997, hundreds of witnesses reported glimpsing signs of extraterrestrial aircraft in the nighttime sky around Phoenix, Ariz., a phenomenon that came to be known as the “Phoenix Lights.” In the world according to “Phoenix Forgotten,” Josh and his friends trekked into the desert to videotape their search for the source of the Phoenix Lights. They were never seen again.

Working from a script he co-wrote with T.S. Nowlin (“The Maze Runner”), first-time feature director Justin Barber shrewdly sustains the first half of his narrative by alternating between vintage home movies of the missing youths and Sophie’s probing interviews two decades later with their parents (including her own divorced mom and dad), people who participated in extensive search parties, and anyone else even tangentially involved with the unsolved mystery. The resulting mashup bears a striking resemblance to a typical episode of “48 Hours” or “Dateline NBC” — an observation that, no kidding, is intended as a compliment.

Unfortunately, “Phoenix Forgotten” takes a detour into drearily familiar territory when Sophie gains possession of a remarkably well-preserved tape discovered inside her brother’s video camera, which was conveniently mailed back to Josh’s school by whoever found it baking under the hot desert sun. Sophie sets up the tape for the audience’s perusal — and then disappears from the movie. She is sorely missed.

Among the many producers of “Phoenix Forgotten,” you’ll find Ridley Scott’s name, which might explain a fleeting wink-wink reference to his “Alien.” But that in-joke isn’t nearly as funny as the brief sequence in which Chelsea Lopez’s Ashley does her impression of Jodie Foster on the verge of a wormhole in “Contact.” The scene is so funny, you may find yourself wishing Barber had filmed Lopez acting out many other highlights from Foster’s oeuvre. That would have been footage worth finding.