We may soon begin to run low on famous cases from the past to reframe into true-crime series. Following on recent series about the Night Stalker and the Ted Bundy murders, Netflix now drops “The Sons of Sam: A Descent Into Darkness,” about the Son of Sam killings in New York City in the late 1970s. That the title and subject differ by a letter is the engine of this story: We follow the late investigative journalist Maury Terry through his belief that the murders, for which David Berkowitz was convicted, have their roots in a grander conspiracy, rooted in a cult with possible ties to other crimes and to the Manson family.

Terry died in 2015, but filmmaker Joshua Zeman had access to his notes and has cast Paul Giamatti to read them in voice-over. The picture that emerges from Giamatti’s committed performance is that of a person who sees deeply under the surfaces of things. Terry was, he tells us, “captivated by the ongoing drama of the .44 Caliber Killer,” as Son of Sam was first known; he wondered “where he would strike next.” This fascination transferred over, once Berkowitz was apprehended, into trying to find the story behind the story, culminating in a rare jailhouse interview with Berkowitz.

The fact of that interview begins to suggest an odd element of “The Sons of Sam”: So much of this has played out in public before. Terry’s fixation was on a possible link between Berkowitz’s killings and Satan worship; we see Maury Povich, Geraldo Rivera, and no less than Tom Brokaw, all in archival footage, reporting along the exact same lines. A TV crime reporter from the era tells us she believes that Terry “wanted to be part of the big story and get the biggest story out of it.” A friend of Terry’s refers to the jailhouse TV interview with Berkowitz that the journalist managed to obtain in 1993 as “the golden fleece.” The fact that this is breathlessly detailed in a documentary nearly 30 years later suggests that Terry ended up being a bigger part of the big story than he might have dreamed.

Much of the function of “The Sons of Sam” is resurfacing elements of a story that has already been part of the public record, and applying to them theories that Terry was never able to prove. (Indeed, the series can’t keep its eye on the ways in which what we know about these killings illuminates a fascinating cross-section of New York City at a moment of change, focusing instead on sweeping fulmination.) That Terry couldn’t finish his work is a sad occupational hazard for a journalist trying to break new ground and dying prematurely; unfortunately, the fact that these are all just theories means that “The Sons of Sam” feels, by the end of its four-hour running time, extravagantly unnecessary. “Whether he could prove it or not, it was still a damn good story,” a friend of Terry’s tells us. Viewers can decide for themselves how true that is.

Or they may tap out beforehand. Like many of its ilk, “The Sons of Sam” is so overlong as to begin to poison the viewer against what is meant to be a sympathetic subject. The recapitulation of the Son of Sam’s deeds is punishing, and what comes after often has the sketchy quality of unfinished notes. (Not for nothing is the archival news footage we see part of what has been called a “Satanic panic,” a culture-wide freakout with limited basis in fact.) Modeling the series around Terry’s work has the unfortunate effect — hardly a new one — of treating the real killings of real people as the jumping-off point for grand theories told with an eye on their power to shock and amaze. Perhaps these victims deserved better.

If anything, the show seems only to find its focus in its final quarter. After running through Terry’s various unproven theories, the series tells the sad story of his physical decline, consumed as he was by trying to crack his case. This seems like the real story here, but Zeman cannot summon more insight than this statement, delivered in voice-over by the director himself: “At times, the world is a dark and rudderless place, and good and evil do exist, but only inside the hearts and minds of us all.”

We’ve come an awfully long way, through a lot of dredging up of trauma and of innocents killed, for a closing statement quite this trite. In its last act, “The Sons of Sam” fumbles what goodwill remained.

The Sons of Sam: A Descent Into Darkness” launches May 5 on Netflix.

Netflix’s ‘The Sons of Sam’ Gets Lost in Fog of Conspiracy: TV Review

Netflix. Four episodes (all screened for review).