According to this account, delivered shortly after the shooting, Judy came home not after Seth returned from the grocery store but before he had left. There is a good reason that Sam and Judy Bishop would be uncomfortable with such a timeline: in their telling, Amy took out the shotgun in the first place because she had been home alone for several hours.

At the inquest, the firearms expert who had examined the twelve-gauge Mossberg testified that it normally takes five pounds of pressure on the trigger in order to fire the gun. “You’re saying the only way it could have gone off accidentally, even if her finger was on the trigger, was if someone was actually pulling it?” he was asked.

“Trying to pull the gun out of her hands,” he responded. “Yeah.”

None of this necessarily indicates that Amy intended to kill her father. She could have been waving the gun around, angry with Sam and wanting to make a demonstration. When I was about fourteen, I once had an argument with my father. It was about some trivial matter—I don’t remember what—but I was furious. We were staying by the ocean, and my father would swim every day, taking long laps parallel to the beach. As he swam that day, I started skipping rocks. I saw him approaching, and continued to pick stones from the sand and hurl them at the waves. Then, suddenly, I heard a howl. My father staggered out of the water, disoriented and alarmed. I hadn’t meant to hit my father—I had intended simply to frighten him, to assert myself somehow. Apart from the shock, it did him no real harm. But it could have. When I told my mother this story recently, she surprised me by saying, “You know, in all these years, your father has never told me about that.”

After I heard the story about Saran Gillies, I went back through Amy’s novels, looking for any further clues that they might hold, and I made a startling discovery. In her first book, “The Martian Experiment,” Abigail White, the protagonist, is haunted by an incident from her childhood. Early in the novel, Abigail is playing with Kathy, a friend from school, and Kathy’s younger brother, Luke. The two girls quarrel, and Kathy throws a rock at Abigail. Overcome by fury, Abigail spies a fist-size rock on the ground and “fires” it into the air, “hoping to make Kathy dodge away in fear.” The rock sails toward Kathy, but it misses her—and lands, instead, on the head of her little brother, Luke.

“He fell back like a toy soldier,” Amy writes. “He never knew what hit him.” Abigail is stunned, “dreading what horror her rock, meant to scare Kathy, had visited upon Luke.” He slips into a coma and dies, and his parents conclude that he must have had an aneurysm.

The passage echoed what seemed to be the most plausible account of Seth’s death: in a fit of anger, a young woman wields a dangerous weapon, intending to frighten one person, but ends up killing another. Abigail is tormented by her actions, and she eventually tries to confess to her grandmother, whom she calls, in the Greek style, Yaya—the name that Amy used with her own grandmother. “I killed Luke,” she says. In a firm whisper, Yaya tells her, “The boy is with God. He knows you are sorry.”

Later, Abigail’s father enters her room, thinking that she is asleep, and kisses her on the forehead. “That one kiss told her that the decision was made and final.” The family will say nothing of her possible responsibility for the death.

When I posed the alternative hypothesis of that day to Amy, she hurried off the phone. The next day, she called back. She denied that the argument with her father had been serious, and offered a different account of it: she had finished a pot of coffee, and Sam had been irritated because “he had to make another pot.” She said, “So I’m not sure where that phone call when Mom said we had a fight came from, because we didn’t,” adding, “Our family always had a very nice relationship.”

Andrew Solomon, in his recent book “Far from the Tree,” writes, in a discussion about how parents cope with children who have killed, “There’s a fine line between heroic love and willful blindness.” Parental denial may be driven by compassion, Solomon argues, but it can also be profoundly confusing for the child. If the child has committed a terrible crime, the parent may refuse to confront it because that feels like the surest strategy for restoring a stable existence. But that very refusal may actually be further destabilizing. In Solomon’s view, it can be “alienating—even traumatic” when parents refuse to acknowledge the horrible things that their children have done. In her novel “Amazon Fever,” Amy Bishop describes the father of her heroine as “willfully blind,” and wonders whether that blindness might make him, on some level, “complicit.” The passage made me wonder about Sam. Had he considered that Amy might have been intent on shooting him? And had he and Judy ever discussed this possibility?

I decided to talk to Judy about the alternative theory, although I wondered if there was much point. “There are only two people who really know what happened in that house,” the woman who related the theory to me said. “And I think Judy has buried it and come up with something she can deal with.” She paused. “And bless her for that.”

She was not alone in this feeling. In speaking with people in Braintree, I was often asked if I had children, as if that might be some prerequisite for grasping the moral calculus at play. “I’ve never asked Sam and Judy what happened in the house that day, because I don’t want them to lie to me,” Judy’s friend Deb Kosarick told me. “And you know what? To protect my kids, I’d lie, too. I’d lie on a stack of Bibles.”

The day before Thanksgiving, I went to see the Bishops again. It was a bitterly cold morning, and smoke curled from their chimney. On December 6th, they had plans to visit Seth’s grave, which is in New Hampshire. It was an annual pilgrimage, and for years Amy had joined them. She would speak to the grave, telling Seth about her life and her children. Even today, she will occasionally call her parents and tell them that Seth has visited her in her jail cell—that he talks to her, and sits on the edge of her bed. Until very recently, Amy told me, she spoke of her brother “in the present tense, or not at all.”

Amy seems unlikely to prevail in her request for a trial in Massachusetts. The decision is up to the district attorney, who appears disinclined to proceed. She has also appealed her conviction in Alabama. This move—which baffled her parents, given that she had pleaded guilty and waived her right to an appeal—also has little chance of success. “The worst thing about prison is being separated from my children,” she told me. Jim, who still lives in Huntsville, has custody of the kids. She speaks to them on the phone as often as she can. Her daughter Phaedra is in the process of selecting colleges. Amy is encouraging her to apply to Harvard.