Adam Lanza had 253 live rounds on his body when police found him dead in the Sandy Hook Elementary School. He killed 26 people, including 20 children in the attack, firing 154 rounds.
He carried nearly 14 kilograms worth of guns and ammunition, a State Attorney report into the Sandy Hook shootings revealed.
All of firearms Lanza used in the attack were purchased legally by his mother, the report said.
A report into the shootings at Sandy Hook Elementary School has concluded gunman Adam Lanza was "undoubtedly afflicted with mental health problems" and had a "fascination with mass shootings".
The report, prepared by the State Attorney, says: "Those who knew the shooter describe him in contradictory ways. He was undoubtedly afflicted with mental health problems; yet despite a fascination with mass shootings and firearms, he displayed no aggressive or threatening tendencies.
"In some contexts he was viewed as having above-average intelligence; in others below-average.
"Some recalled that the shooter had been bullied; but others – including many teachers – saw nothing of the sort. With some people he could talk with them and be humorous; but many others saw the shooter as unemotional, distant, and remote."
A State Attorney report into the Sandy Hook shootings has now closed and has ruled out any criminal prosecutions.
Adam Lanza, the gunman who killed 20 children and six adults in an elementary school shooting in Connecticut, acted on his own, a year-long inquiry into the massacre has ruled.
The report, published today, admitted that questions about Lanza's motive may "never be answered conclusively."
Actor Jim Carrey has withdrawn his support from Kick-Ass 2, in which he stars, stating he can no longer "support that level of violence" in light of the Sandy Hook shooting.
Carrey - a well-know advocate of gun control - made the statement on Twitter on Sunday night:
I did Kickass a month b4 Sandy Hook and now in all good conscience I cannot support that level of violence. My apologies to e
I meant to say my apologies to others involve with the film. I am not ashamed of it but recent events have caused a change in my heart.
20 children and six teachers were killed when Adam Lanza fired 155 bullets in less than five minutes at Sandy Hook Elementary School last December.
The 51-year-old stars as Colonel Stars and Stripes, the leader of a group of superheroes, in the film which is due to be released in the UK on 14 August.
Mark Millar, the creator of the original comic book and the executive producer of the film, said he was "baffled" by Carrey's decision and urged him to reconsider.
Six months ago today, 26 families in Newtown were torn apart by gun violence—and Congress has done nothing. Shame on us if we've forgotten.
For young people in parts of America, guns are a normal and regular part of everyday life.
Mallory Tate, 12
"I got my first gun when I was five or six. I went on safaris in Africa and as I grew up went on rabbit hunts.
"Even when I go to school I can have a conversation with my best friend about a gun or what I shot this weekend."
Morgan Lingdon, 13
"This is such a big part of my life. I shoot every Thursday night and I'm going to be shooting every weekend. I just love the sport."
Former British newspaper editor Piers Morgan, who is now a TV host for US network CNN, said he has become "increasingly angry" at the number of Americans killed in gun murders.
"In Britain we have between 30 and 50 gun murders a year," he explained. "In America they have 11-12,000 murdered with guns every year. Another 18,000 people kill themselves with guns every year."
As part of his documentary exploring America's love affair with firearms, ITV News Washington correspondent Robert Moore fired an AR-15 assault rifle for the first time.
The names of 20 children and their six teachers were read out today, six months after they were shot dead at Sandy Hook in one of America's worst school shootings.
Since the school massacre, thousands more people have died from gun crime in the US.
The parents of the children killed in December are still fighting for a change in gun laws.
This report is by ITV News Washington correspondent Robert Moore:
A special Tonight: America and its Guns was broadcast at 19.30pm on ITV