Former student Adam Lanza, who authorities said opened fire inside the Sandy Hook Elementary School in Newtown, Connecticut, killing 26 students and educators.

Former student Adam Lanza, who authorities said opened fire inside the Sandy Hook Elementary School in Newtown, Connecticut, killing 26 students and educators. Photo: AP

A summary of the investigation into the massacre of 26 children and staff at Sandy Hook Elementary School has been released, confirming that the shooter, Adam Lanza, acted alone and adding new details of the heroism of staff and police, who investigators have credited with saving many lives.

The report summary appears to deliberately dismiss widespread conspiracy theories about the attack, but casts no light on Lanza's motives.

"The evidence clearly shows that the shooter planned his actions, including the taking of his own life, but there is no clear indication why he did so, or why he targeted Sandy Hook Elementary School," says the report. "He had a familiarity with and access to firearms and ammunition and an obsession with mass murders, in particular the April 1999 shootings at Columbine High School in Colorado."

Officials standing outside of Sandy Hook Elementary School in Newtown, Connecticut in December 2012. A report on the Newtown school shooting says that gunman Adam Lanza had an obsession with mass murders but that investigators did not discover any evidence he had indicated to others an intention to carry out such a crime.

Officials standing outside of Sandy Hook Elementary School in Newtown, Connecticut in December 2012. Photo: AP

The report describes how one staff member ran towards the school lobby after hearing a crashing noise, and on arriving saw bullet holes and smelt gunpowder. The staff member called 911 and stayed on the phone throughout the incident, clearing corridors and running from room to room to give warning of the attack and locking doors behind him.

The summary does not named the person, though earlier reports suggest this was a school janitor, Rick Thorne, who was invited to the White House for a memorial service in February.

The official summary confirms earlier reports that Lanza shot his way through the school's locked security door at around 9.35am. He then shot dead the school principal, Dawn Hochsprung, and a counsellor, Mary Sherlach, who had apparently come to investigate. There he shot and wounded two more staff members.

Emilie Parker was one of 20 children shot dead at Sandy Hook Elementary School in 2012.

Emilie Parker was one of 20 children shot dead at Sandy Hook Elementary School in 2012. Photo: AP

He then entered the school office, where he did not find staff in hiding. He returned to the hallway, entering two first grade classrooms. In classroom eight he killed 15 children and two adults, in classroom ten he killed five children and two adults before killing himself.

Earlier reports suggest that in this room his gun jammed and during the pause in firing a student, Jesse Lewis, shouted for his classmates to run. Six escaped though Jesse was shot dead. The class teacher, Victoria Soto, had already been killed as she sought to shield her students.

The official summary confirms the whole attack took around five minutes, during which time Lanza fired 154 rounds from a semi-automatic Bushmaster rifle, killing 20 children and six adults, before shooting himself dead with a single shot with a Glock semi-automatic pistol.

Police arrived at the school in 3 minutes and 21 seconds and entered the school 4 minutes and 44 seconds after the last shot is heard.

Lanza had shot dead his mother, Nancy Lanza, sometime before he went to the school. According to the report she had legally purchased all the weapons and ammunition he used in the attack.

The report apparently seeks to provide information to contradict the many conspiracy theories that now surround the massacre. It explains how at 9.39am Newtown police officers detained an unknown male running along the school property with something in his hand. They soon determined he was a parent holding a mobile phone, but early media reports of the man's detention have become a focus for the conspiracies.

The report summary's publication has been the subject of controversy in Newtown. Its author, State Attorney Stephen Sedensky, has been criticised for preventing the full publication, delaying the publication of the summary, and refusing to release crime scene photographs and 911 recordings.

It has been argued that Sedensky's reticence to make details of what went on in the school public has fed conspiracy theorists, many of whom believe the massacre was staged by the government to justify gun control laws.

When directed by the Connecticut Freedom of Information Commission to release 911 call tapes to media in September Sedensky appealed the decision using child protection laws.

He appealed to the judge to consider the anguish the tapes could cause the families of the dead children.

A free speech lawyer, Daniel Klau from Connecticut's nearby capital, Hartford, has argued Sedensky might be overstepping the mark.

"It's almost as if he is behaving like a private attorney for the Sandy Hook families," Klau told the Hartford Courant. "The state's attorney is not private counsel for the victims and families. That is troubling.

The Courant wrote in an editorial that, "The State's concern now must be with protecting schools rather than feelings, much as our hearts go out to the victims' families.

"Connecticut needs to know why Adam Lanza murdered and what can be done to keep loved ones safe from another madman."

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