How can you make a film that you don’t have official permission to actually make? A convincing answer to this query is the existence of Charlie Shackleton’s baldly titled Zodiac Killer Project, premiering in Sundance’s NEXT strand, which reexamines the legendary unsolved US homicide case of the eponymous killer. Driven by his own wry and quizzical voice-over, this absorbing film-essay is self-compensation for Shackleton being unable to make an authorised adaptation of Lyndon E Lafferty’s dramatically named The Zodiac Killer Cover-Up: The Silenced Badge (one can imagine a 1960s TV announcer declaiming the title, like from Once Upon a Time… in Hollywood), a true-crime doorstopper already overshadowed by Robert Graysmith’s original 1986 exposé, the inspiration for David Fincher’s classic film. Near the start, Shackleton confesses that he happened upon the former through Amazon’s trusty algorithm, which sets the playful, humblebrag-like tone.

Zodiac Killer Project also pivots on a contradiction that numerous films invoke, but this one gets closer than most to reconciling it: that of being a rejoinder to our media-consumption pathologies, whilst also being a prime example of the same. Given Lafferty’s crusade, beginning as a highway patrol cop in Solano County, northern California, who chances upon vague overlaps in the life of his main object of suspicion, George Russell Tucker, with concrete evidence from the Zodiac’s five accounted-for murders, Shackleton is neatly poised between laughing at and judging someone in over their head and identifying as an artist with his dogged determination and ethically challenging acts of vigilantism. Lafferty may have been a lousy sleuth, but he’s a great and pathos-inducing potential movie character, and the director wants to honour that, whatever his lawyer’s guidance (amusingly paraphrased in the voice-over) says.

Zodiac Killer Project is a low-fi, DIY affair whose end-credit tally of clips from the true-crime series shown in the pseudo-“film criticism” segments is almost equal to its production personnel. The visual and narrative schema merely involves Shackleton narrating the botched tale of his would-be debut feature and going into detail on key sequences from the book, alongside attractive travelling wide shots (credit to DoP Xenia Patricia) of the Solano locations in question, whether they’re ominous or just benign-seeming masters of curling highways, rest stops, strip malls and photogenic, multi-story homes shrouded by the area’s unique foliage. The title and philosophy of Jafar Panahi’s This Is Not a Film also comes to mind: Shackleton’s movie often feels like a 90-minute disclaimer that it shouldn’t be mistaken for a “real film”, yet by definitions of quality, it’s undoubtedly that.

Shackleton further twists the analytical knife as he expounds on the methods and grey areas of true-crime phenomena like The Jinx, the Paradise Lost trilogy and Netflix’s Making a Murderer, observing how their respective filmmakers’ authorial control can potentially mislead the audience away from likelihood and rationality towards misleading assertions. When the director in voice-over muses on how he would have reconstructed a bizarre sting operation where Lafferty would capture Tucker’s handprint on a fishbowl, it’s oddly bittersweet when he exclaims, “It would’ve been so good,” sounding like a stroppy child dissuaded from unleashing firecrackers indoors. And there, he indicts and cements the appeal of endlessly proliferating true-crime content, which he laments has swallowed up the documentary industry to which he’s dedicated his whole filmmaking career.

Zodiac Killer Project is a production by the UK and the USA, staged by Loop with involvement from Field of Vision. Its world sales are overseen by Cinetic.