MERIDEN/NEWTOWN, Conn. - The gunman who killed 20 children and six adults at a Connecticut elementary school fired 154 rounds in less than 5 minutes, selecting high capacity magazines from a home arsenal stocked with swords, knives and a cache of guns, officials said.

Investigators also found a newspaper clipping about a mass shooting in the home that Adam Lanza shared with his mother, along with a gun safe in his bedroom, receipts from shooting ranges and National Rifle Association certificates for both of them, according to court papers released on Thursday.

To carry out the second deadliest school shooting in US history, Lanza used 30-round magazines at Sandy Hook Elementary School in Newtown, said Connecticut Governor Dannel Malloy after the previously sealed searches of Lanza's car and home were made public.

The home of Nancy Lanza and her son Adam in Newtown Connecticut, on March 28, 2013. Adam Lanza, the gunman who killed 20 children and six adults at a Connecticut elementary school fired 154 rounds in less than 5 minutes, selecting high capacity magazines from a home arsenal stocked with swords, knives and a cache of guns, officials said. [Photo/Agencies]

"We now know that he left the lower capacity magazines at home," Malloy said in a statement. "This is exactly why we need to ban high capacity magazines and why we need to tighten our assault weapons ban."

As more details about the shooting came to light, US President Barack Obama urged with US lawmakers not to forget those shot to death in Newtown three months ago.

"The entire country pledged we would do something about it and that this time would be different. Shame on us if we've forgotten," said Obama, appearing at the White House with mothers of children who had been shot to death.

The Dec 14 rampage started at the Lanza family home, where authorities say the 20-year-old shot dead his mother, Nancy Lanza, and then drove to the school he once attended. Armed with an AR-15-type assault rifle and two handguns he killed the 20 children, six staff members and himself.

The pale yellow two-story suburban colonial house where Lanza lived is directly across the street from the home of Dylan Hockley, 6, who died in his teacher's arms in the massacre. The Hockley family has since moved to another part of town.  

Searches of the house by police turned up a cache of guns, three samurai-style swords and boxes of bullets, along with items that could offer some clues on Adam Lanza's thinking.

Among them were a 2008 New York Times clipping on an Illinois school shooting and books on Asperger's syndrome and autism. Friends of the Lanza family had described Adam Lanza as having Asperger's syndrome, which is a form of autism.

For some in the tight-knit southern New England town, the release of the new details only inflamed emotional wounds.

"We struggle every day to stay on the path of recovery and every bit of information that becomes part of the public discourse holds a potential hurt for a family who has already suffered immeasurable harm," said Newtown First Selectman E. Patricia Llodra.

The attack, which Obama called the worst day of his presidency, reignited a fierce debate on gun violence and gun regulation in the United States. The Second Amendment of the US Constitution protects the right to gun ownership.

The National Rifle Association called after the shooting for armed guards to patrol public schools, while gun-control advocates called for tighter restrictions on both the process to buy guns and the types of guns and ammunition clips that may be sold.