Remembering Sandy Hook: A 4-year anniversary timeline of the day's horrific events

On Dec. 14, 2012, 20-year-old Adam Lanza entered Sandy Hook Elementary School in Newtown, Conn., where he shot and killed 20 children and six women. To this day, the incident remains the deadliest mass shooting at a high school or grade school in U.S. history.

The tragic events start at 9:30 a.m. when Lanza enters the school building and end when the shooter takes his own life at 9:40 a.m. It was fewer than five minutes from the time the first 911 call was received until the Lanza killed himself.

Per a report released by a Connecticut state attorney, here is a timeline of the painfully tragic events that flatlined a community and devastated the nation.

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9:30 a.m.: A parent is buzzed in through the front doors for a holiday gingerbread event.

9:30 a.m.: Adam Lanza approaches the front entrance to the school. He was armed with a Bushmaster Model XM15-E2S rifle (also Bushmaster rifle), a Glock 20, 10 mm pistol and a Sig Sauer P226, 9 mm pistol and a large supply of ammunition.

9:34 a.m.: The first gunshots are heard. Witness later reports hearing about 15 shots.

9:35 a.m.: Main office staff report hearing noises and glass breaking at the front of the building.

9:35:39 a.m.: The first 911 call is received at Newtown Police Department. Someone calling from the school nurse's office says she saw the shooter.

At some point during this timeframe, these events occurred:

- While in a 9:30 a.m. Planning and Placement Team meeting, attendees hear a loud bang. Principal Dawn Hochsprung and School Psychologist Mary Sherlach leave the room, yelling for people to "Stay put!" A staff member witnesses Hochsprung and Sherlach's being shot. Both 47-year-old Dawn Hochsprung and 56-year-old Mary Sherlach were killed that day.

- A witness who is shot makes her way to a room where she calls 911 and turns on the school-wide intercom system. This provides notice to other portions of the building.

- Evidence and witness statements establish that Lanza eventually entered two first grade classrooms, killing 20 children and four adults between those two rooms.

- Twelve children survived, one from classroom 8 and eleven from classroom 10.

9:35:56 a.m.: Newtown police are informed of shooting. Over the next minute, several officers head toward school.

9:36 a.m.: Unidentified witness arrives at school. Upon seeing broken glass and hearing gunfire she takes shelter behind a trash receptacle and call 911.

9:37:38 a.m.: State Police dispatch advises units of shooter, and units head to school.

9:40 a.m.: A final gunshot is heard, believed to be Lanza's final suicide shot.

9:41 a.m.: Officer detains individual near school playground; police advised to be on look out for possibility of second shooter.

9:44 a.m.: Three Newtown officers enter Sandy Hook Elementary school through boiler room.

9:45 a.m.: Bodies of two victims found. Officer radios for assistance: "OK, I need units in the front of the school. I've got bodies here. Let's get ambulances."

9:46 a.m: Officers enter building through front of school.

9:47 a.m.: Police set up perimeter and begin evacuating children.

9:51 a.m.: Lanza's body is found by police.

10:10 a.m.: State Police sergeant radios dispatch, "We have multiple, in the double digits, of death here ... so it's not good ... we have, we're still clearing rooms ... we have one suspect ... one suspect down ... deceased."

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