Nancy Lanza

The Sandy Hook Elementary School shooting was a mass shooting that occurred on December 14, 2012, in Newtown, Connecticut, United States, when 20-year-old Adam Lanza shot and killed 26 people.

Twenty of the victims were children between six and seven years old, and the other six were adult staff members.

Earlier that day, before driving to the school, Lanza fatally shot his mother at their Newtown home.

As first responders arrived at the school, Lanza died by suicide, shooting himself in the head.

The incident is the deadliest mass shooting in Connecticut history and the deadliest at an elementary school in U.S. history.

The shooting prompted renewed debate about gun control in the United States, including proposals to make the background-check system universal, and for new federal and state gun legislation banning the sale and manufacture of certain types of semi-automatic firearms and magazines which can hold more than ten rounds of ammunition.

As of November 30, 2012, 456 children were enrolled in kindergarten through fourth grade at Sandy Hook Elementary School.

The school's security protocols had recently been upgraded, requiring visitors to be individually admitted after visual and identification review by video monitor.

Doors to the school were locked at 9:30a.m. each day, after morning arrivals.

Newtown is in Fairfield County, Connecticut, about 17 mi from New Haven, 30 mi from Hartford, and 60 mi from New York City.

Violent crime had been rare in the town of 28,000 residents; there was only one homicide in the town in the ten years before the school shooting.

Under the Connecticut gun laws at the time, the 20-year-old Lanza was old enough to carry a long gun, such as a rifle or shotgun, but too young to own or carry handguns.

The guns he used had been purchased legally by his mother.

Sometime before 9:30a.m. EST on December 14, 2012, Lanza shot and killed his mother Nancy Lanza, aged 52, with a .22-caliber Savage Mark II rifle at their Newtown home.

Investigators later found her body clad in pajamas, in her bed, with four gunshot wounds to her head.

Lanza then drove to Sandy Hook Elementary School in his mother's car.

Shortly after 9:35a.m., armed with his mother's Bushmaster XM15-E2S rifle and ten magazines with 30 rounds each, Lanza shot his way through a glass panel next to the locked front entrance doors of the school.

He was wearing black clothing, yellow earplugs, sunglasses, a black hat, and an olive green utility vest.

Initial reports that he was wearing body armor were incorrect.

Some of those present heard the initial shots on the school intercom system, which was being used for morning announcements.

Principal Dawn Hochsprung and school psychologist Mary Sherlach were meeting with other faculty members when they heard, but did not recognize, gunshots.

Hochsprung, Sherlach, and lead teacher Natalie Hammond went into the hall to determine the source of the sounds and encountered Lanza.

A faculty member who was at the meeting said that the three women called out "Shooter! Stay put!"

which alerted their colleagues to the danger and saved their lives.

An aide heard gunshots.

A teacher hiding in the math lab heard school janitor Rick Thorne yell, "Put the gun down!"

Lanza killed both Hochsprung and Sherlach.

Hammond was hit first in the leg, and then sustained another gunshot wound.

She laid still in the hallway and then, not hearing any more noise, crawled back to the conference room and pressed her body against the door to keep it closed.

She was later treated at Danbury Hospital.

A nine-year-old boy said he heard the shooter say "Put your hands up!"

and someone else say "Don't shoot!"

He also heard many people yelling and many gunshots over the intercom while he, his classmates, and his teacher took refuge in a closet in the gymnasium.

Diane Day, a school therapist who had been at the faculty meeting with Hochsprung, heard screaming followed by more gunshots.

A second teacher, who was a substitute kindergarten teacher, was wounded in the attack.

While she was closing a door further down the hallway, she was hit in the foot with a bullet that ricocheted.

Lanza never entered her classroom.

A November 2013 report issued by the Connecticut State Attorney's office concluded that Lanza acted alone and planned his actions, but provided no indication why he did so, or why he targeted the school.

A report issued by the Office of the Child Advocate in November 2014 said that Lanza had Asperger's syndrome and, as a teenager, depression, anxiety, and obsessive-compulsive disorder, but concluded that they had "neither caused nor led to his murderous acts".

The report went on to say, "his severe and deteriorating internalized mental health problems[...] combined with an atypical preoccupation with violence[...] (and) access to deadly weapons[...] proved a recipe for mass murder."