Almost from the beginning, Lizzie, 32, was the only serious suspect. The Fall River police began their search by concentrating on local immigrants, but an outsider seemed improbable. Lizzie and the housemaid (who had an alibi) were both home; how would a stranger have escaped notice during the murders — and the time between them? Other sinister details emerged: Lizzie was reportedly seen trying to buy highly poisonous prussic acid the day before the killings.

The case seized the town like a sickness. “Where to Look for Your Wife” ran a headline in the Fall River Daily Globe, over an item describing the “crowd of morbid females who are storming the door of the county court house.” Some locals called for the mystery to be solved lest the town go insane. The murders were especially disconcerting not just because they were so savage and intimate, but because Lizzie’s arrest “unsettled an ethnically and class-determined model of criminality,” Robertson writes. In the public imagination, the white, Christian daughter of a powerful scion was considered morally incapable of such crimes.

Identity — Lizzie’s gender, in particular — became the bedrock for the cases made by both prosecution and defense. “The youngest daughter?” her lawyer petitioned. “The last one whose baby fingers have been loving entwined about her father’s head. Is there nothing in the ties of love and affection?” The prosecution, meanwhile, pointed to the nature and number of the blows, clearly committed by “an irresolute, imperfect feminine hand.” The conspicuously unnerved judge was forced to employ a thought experiment: “Suppose for a single moment that a man was standing there,” he said. “Would there be any question in the minds of men what should be done with such a man?”

“Most interpretations tell us more about the preoccupations of its chroniclers than any essential truth about the mystery,” Robertson writes. In the 1950s, Lizzie Borden was resurrected as a feminist heroine. As one book from that period put it: “If today woman has come out of the kitchen, she is only following Lizzie, who came out of it with a bloody ax and helped start the rights-for-women bandwagon.” In the 1990s, another theory surfaced: that Lizzie murdered her parents after years of sexual abuse by her father. This theory relied on the fact that their bedrooms were connected by a door, the intensity of their relationship and the detail that instead of a wedding ring, Andrew wore a gold ring given to him by Lizzie.

Every generation reframes the story in the light of its signal preoccupations. Robertson does, too, and openly. She refers to young adult novels and films that have offered more fully realized portraits of Lizzie, as well as documentaries like “The Staircase” and “Making a Murderer,” which relitigate old cases with fresh evidence. She also might have mentioned recent documentaries on Tonya Harding and Lorena Bobbitt— women whose stories are now being scrutinized with more subtlety, and with an eye to how sexism shaped their public narratives.

Robertson is a scrupulous writer who stays tethered to the archives, but I often wished she had permitted herself to rove more freely, to speculate and imagine. The real riddle of Lizzie Borden isn’t whether she did it, or why, but can be found in the dark fascination she continues to exert. She remains as elusive in this admirable book as in life, as in the photographs that remain to us — a round-cheeked young person with a decisive mouth, not quite meeting our eye.

“There seems to be little prospect that the mystery will be cleared up by the trial,” this newspaper commented prophetically in 1893. “The verdict, if there shall be a verdict, will make little difference.”