Last week US federal prosecutors announced a woman had been indicted for making death threats against a parent whose child was murdered in the 2012 mass shooting at Sandy Hook elementary school. Her motivation, the US Department of Justice said, was her belief that the massacre never happened, that it was a hoax.

Wednesday marks four years after the massacre in Newtown, Connecticut, happened, and still, just the name Sandy Hook carries a terrible power around the world, capable of delivering an emotional gut punch. In a country where mass shootings are all too common and gun violence takes a daily toll, the shooting of 20 young children in their classrooms, along with six staff members who desperately tried to protect the little ones in their care, still stands out as a particular horror. As The New York Times pointed out, Sandy Hook has also become a symbol of American political intransigence on gun control, shorthand for the "culture of shameful inaction that has taken hold in the wake of the shooting", a period in which no major gun control legislation has received congressional support.

But this year in particular, the anniversary of Sandy Hook is also, unfortunately, a reminder of another kind of ugliness that is having a cultural moment – the proliferation of mad conspiracy theories and paranoid fantasies online, which are spilling from the dark fringes of the internet into the mainstream and in some cases, causing real damage.

A small but vocal cohort of people – who ironically call themselves "truthers" – has long tried to muddy the record of what happened at Sandy Hook – variously pushing the notion that the rampage in Newtown was a hoax staged with actors and that no one actually died, or at the least, that key details such as who was responsible were fabricated as part of a plot to manipulate the American public.They believe the perpetrators of this plot are "gun grabbers" – be it the Obama administration, the media or others – who are so intent on depriving Americans of their guns they would falsely stage the mass murder of children to make their point, drawing a town, law enforcement and the rest of the world into an elaborate fiction.