This morning, the Sandy Hook Elementary School in Newtown, Conn., was full of children thinking about Christmas lists and gifts. Then, at 9:40 a.m., countless shots reportedly rang out.
Here is a timeline of the massacre at the grade school today, and the events that followed:
9:40 a.m.: Shooting reported to state police. State troopers descend on the scene, as well as federal agents from the FBI and the Bureau of Alcohol Tobacco and Firearms.
"Sandy Hook school. Caller indicating she thinks someone is shooting in the building," is heard over the police radio.
11 a.m.: Police give the first indications that there are multiple fatalities inside. Fifty minutes later, they announce that most of the dead are children.
"Units in the school. I got bodies here," is heard over the police radio.
11:52 a.m.: Danbury Hospital confirms three patients have been taken there for treatment.
11:55 a.m.: Danbury Mayor Mark Boughton tells WABC-TV that the three hospitalized victims are in "very serious condition."
12:09 p.m.: Sources tell ABC News multiple people were shot.
12:19 p.m.: Federal agents are at the scene, with guns still drawn, as parents rush to pick up their children.
12:24 p.m.: Law enforcement agents with weapons drawn seen running into wooded area behind the school.
12:26 p.m.: Federal and state law enforcement sources tell ABC News that more than a dozen people, including children, were fatally shot at Sandy Hook Elementary School, .
12:36 p.m.: Law enforcement conducts car-to-car searches in area of school.
12: 47 p.m.: More than 20 people, most of them young children, killed in elementary school shooting, according to law enforcement sources.
12:57 p.m.: Number of fatalities continues to rise. More than 25 people, mostly young children, killed in Newtown, Conn., school shooting, sources tell ABC News.
1:08 p.m.: ABC News reports death toll has risen to 27.
Approx 1:10 p.m. Sources tell ABC News that one shooter was 24 years old, armed with four weapons and wearing a bullet-proof vest. Police looking for a possible second shooter.
1:25 p.m.: President Obama is briefed by FBI Director Bob Mueller and speaks with Connecticut Gov. Dan Malloy to discuss the attack and express his condolences.
1:41 p.m.: State police hold a news conference on the Connecticut school shooting. Police say deaths included students and staff at Sandy Hook Elementary.
2:27 p.m.: ABC New reports that authorities have identified the shooter as Ryan Lanza of New Jersey. Authorities also say that a dead body has also been found in his home.
2:36 p.m.: ABC News reports the gunman's mother, a kindergarten teacher, was among the dead found inside the school.
3:15 p.m.: President Obama holds a news conference and orders that U.S. flags be flown at half-staff until Dec. 18, 2012. "Our hearts are broken today," he says.
4:11 p.m.: ABC News reports that 20 children were killed in the Newtown, Conn., school massacre. Eighteen children are pronounced dead at the school; two, at the hospital; and six adults, at the school, Connecticut State Police spokesman Paul Vance says.
4:37 p.m.: ABC News reports that federal officials say that the gunman in the shooting is actually Adam Lanza, the brother of Ryan Lanza.
5:28 p.m.: ABC News clarifies that Adam Lanza's mother is not a teacher but a teacher's aide at Sandy Hook. An unidentified woman was found dead at the Lanza's Connecticut home nearby. The relationship with that woman and the shooter is unclear.
6:25 p.m.: ABC News reports that Adam Lanza's mother, Nancy Lanza, was killed in her home. Sources say Adam Lanza shot his mother in the face, then left the house armed with at least two semiautomatic handguns and a semiautomatic rifle, and then drove to Sandy Hook Elementary and killed 20 students and an additional six adults.