Addressing the bereaved community of Sandy Hook last week, President Obama read the names of Adam Lanza's victims – all 26. On the one-week anniversary of America's second-most lethal school shooting, bells tolled across the nation – 26 times. But even omitting his suicide, the impenetrable killer's victims numbered 27.

American education has not so deteriorated that even the president can't count. The discreetly deleted fatality was Adam's first and no doubt primary target: his mother, shot in her bed, four times in the head. Yet grief on Nancy Lanza's account has been stinting. With funerals of children and teachers standing-room-only, Nancy's service last Thursday drew a sparse two dozen relatives.

According to the script in progress, Nancy Lanza doesn't deserve our tears. Implicitly or explicitly, we blame Adam's mother for his baffling rampage – if only for keeping five weapons in her home, four of which her son appropriated. Echoing similar sentiments all over the web, one White House Twitter follower wrote of Nancy, "RIP, but she's culpable".

Let's set aside European disapproval of civilians bearing arms, ever. If only by a circular definition, whereby anyone who systematically massacres 20 first-graders is ipso facto crazy, Nancy Lanza's 20-year-old was not well. On the face of it, then, was keeping guns in her house gross negligence? In which case, one more time, we get to demonise the mother.

Sandy Hook has been the most misreported story in recent memory, but a few facts may have emerged. To date, authorities have not located any confirmed diagnosis for Adam Lanza. Relatives and former classmates say he had Asperger's syndrome, but this mild form of autism has no correlation with violence. The boy is described as anything but menacing – rather, as withdrawn, antisocial, even "meek", according to an official at his high school, who explained that Adam was only assigned a psychologist because a scrawny, cringing loner might be tormented by peers.

Yet a Mail Online comment questions "why a mom with a clearly disturbed son, who most likely had committed other acts of violence (probably in the privacy of his own home) would stock such an arsenal". After all, when the facts don't bolster your viewpoint, you can always make them up. For Adam had no criminal record. Beyond 10-year-old temper tantrums – typical for Asperger's children – we lack even hearsay evidence that this kid was ever violent before. No one claims there were "warning signs".

Even the oft-printed assertion that Nancy frequently took her sons to shooting ranges is not bearing scrutiny. At a nearby range, police pored for hours over every sign-in, and found no Lanza at target practice in 2012.

Nevertheless, Nancy Lanza has been disparaged from the start. Multiple stories have pegged her as a "prepper" – a survivalist gearing up for economic collapse by stocking weapons and tinned food. Yet this gonzo tag hails from a single, biased source, Nancy's sister-in-law, and has since been contradicted by friends. An acquaintance said she seemed "high-strung" – an opaque and prospectively neutral adjective that went viral, repeated to insinuate that the mother herself might have been unbalanced. And tut-tut: she never seemed eager to invite neighbours into her home.

Much of what we now know about Nancy is none of our business: the square footage of her house, the size of her alimony payments. For the purpose of deciding whether her murder is worthy of our mourning, it is our business whether her son was overtly unhinged, so should never have been living in a household with guns.

Unnervingly, to our knowledge Adam Lanza never gave any outward expression to the malice festering in his head. Before that awful Friday, he wouldn't have appeared necessarily more dangerous than any other shy, quiet young man.

Around 270 million weapons in the US are kept legally in private hands. Presumably, a good proportion of American gun owners have families – including college-age boys still living at home. Every such American is thus guilty of the exact same dereliction as Nancy Lanza was. Do they all deserve to die? Indeed, any gun owner assumes the risk that the weapon will be misused, perhaps to horrific effect.

Sure, bring on the gun control debate. But Nancy Lanza is a scapegoat. A vibrant woman of 52 was killed in Connecticut, and her death might have merited at least one damn bell toll.