Of all the mass shootings to have scarred the American consciousness in recent years, the one at Sandy Hook stands out for its child victims: 20 young lives cut short inside their elementary school classroom.
Five years later, the wounds are still gaping.
At 9:30 am on Thursday, the bells of the St. Rose of Lima church in Newtown, Connecticut rang out 26 times, one chime for each life lost, as the small community came together in remembrance.
At the same hour, on December 14, 2012, a 20-year-old named Adam Lanza burst into the brick school building in Newtown armed with a Bushmaster AR-15 assault rifle and two pistols. Earlier that morning, he had shot and killed his own mother at home.
He fired more than 150 times in the corridors and classrooms, killing 20 children between the ages of six and seven, and six women who worked at the school, before committing suicide.
"FIVE. YEARS. The hurt is the same. The suffering. The missing. The heartbreak. The sadness," tweeted Erica Lafferty, whose mother the school principal Dawn Hochsprung was killed trying to stop the shooter. "Nothing will ever fill this void."
In an America already traumatized by previous school shootings, at Columbine High School in Colorado or Virginia Tech university in Virginia, Sandy Hook was a shock: it was the first to target children so young.
"People ask me: how is Sandy Hook doing today? said Chris Murphy, a senator from the small New England state.
"Sandy Hook will never recover, Sandy Hook will never be the same."
- Obama's tears -
Barack Obama, then nearing the end of his first term in office, shed tears as he addressed the shooting from the White House a few hours later.
"We're going to have to come together and take meaningful action to prevent more tragedies like this, regardless of the politics," said Obama, who would later describe the massacre as the worst day of his presidency.
But for those hoping that Sandy Hook would push lawmakers to enact tougher restrictions on guns, the years after the shooting brought disappointment.
Post-Sandy Hook gun control legislation was defeated in Congress in April 2013, and virtually nothing has changed since then, beyond local measures taken by cities and states.
"America needs common-sense gun laws more than ever and we must not stop pushing until we get them," tweeted the former president Bill Clinton on Thursday, as he paid tribute to the victims five years on.
What Sandy Hook did bring, however, was a new awareness by schools across the United States of their vulnerability.
Since 2012, alert procedures and drills have multiplied. Doors and windows are reinforced, and schools have closer ties with police.
American schoolchildren are now taught how to respond to an "active shooter" situation, and staff are trained on how to barricade their classrooms.
- Better school security -
Recent events have illustrated the importance of these steps: when a man killed five people in rampage in northern California in November, he attempted to gain access to an elementary school but was unsuccessful.
It only took about 50 seconds for the school to go on lockdown, helping to avert a potential bloodbath.
Sandy Hook also gave rise to new organizations that take aim at gun violence in the US, which kills 90 people per day.
One such group, Sandy Hook Promise, works to prevent shootings by identifying warning signs, such as young people in a situation of social isolation or showing a fascination with morbid ideas.
In a sinister twist, the shooting has also sparked flourishing conspiracy theories -- purveyed by some opponents of gun control -- who claim the massacre was staged.
A professor at a Florida university, fired from his job after insisting Sandy Hook was a hoax, lost a lawsuit this week claiming that his right to free speech was infringed.
But Lafferty, the principal's daughter, says she has suffered five years of online attacks by conspiracy theorist trolls, and the abuse continued the day of the shooting anniversary.