US President Barack Obama attended a memorial service for the victims of the Sandy Hook school massacre as churches opened their doors to comfort a grieving town.

Mr Obama's visit to Newtown for an interfaith vigil was the fourth time he has travelled to a city after a mass shooting.

The bloodbath brought despair and horror to the New England community, 60 miles north east of New York City, preparing for the Christmas holidays.

It emerged Adam Lanza, 20, shot his mother Nancy multiple times in the head according to the Coroner's Office.

A Connecticut official said Lanza had shot his mother four times in the head. She was found in bed wearing pyjamas.

One of the 20 child victims was a British schoolboy Dylan Hockley.

The six-year-old, one of eight boys and 12 girls in First Grade gunned down in cold blood by Lanza, is believed to have been born in Britain and only moved to Newtown, Connecticut with English father Ian, American mother Nicole and his elder brother Jake in January 2011.

In a feature for the local paper the Newtown Bee, believed to have been published earlier this year, Mrs Hockley said they lived in England for 18 years, where her husband worked for IBM, before moving to the Connecticut town, where they were "happy and comfortable".

"Newtown is a wonderful place to live and we're looking forward to being here a long, long time," she told the paper.

She added: "Being with my children is much more rewarding than I thought it would be, coming from a big career background. Spending time with my children gives me a lot of joy."

In one of America's worst school shootings, Lanza killed 20 children, all first graders aged six or seven, who were shot up to 11 times each.

He also killed six women, including school head Dawn Hochsprung, before turning the gun on himself. His mother Nancy was also found shot dead at their home in the town.

Lanza committed suicide as first responders closed in, the governor said, raising the spectre that Lanza had planned an even more gruesome massacre and was stopped short.

Lanza blasted his way into the Sandy Hook Elementary School and used a high-power rifle to kill 20 children and six adults, including the principal and school psychologist who tried to stop him, authorities said.

As Mr Obama prepared to visit and churches opened their doors to comfort a grieving town, federal agents fanned out to gun stores and shooting ranges across Connecticut, chasing leads they hoped would cast light on Lanza's life.

Among the questions: Why did his mother, a well-to-do suburban divorcee, keep a cache of high-power weapons in the house? What experience did Lanza have with those guns? And, above all, what set him on a path to shoot and kill 20 children, along with the adults who tried to stop him?

Governor Dannel Malloy said Lanza shot himself as police entered the building.

He said: "We surmise that it was during the second classroom episode that he heard responders coming and apparently at that, decided to take his own life."

Malloy offered no possible motive for the shooting and a law enforcement official has said police have found no letters or diaries left behind that could shed light on it.

Lanza shot dead his mother Nancy at the home they shared on Friday, then drove to Sandy Hook Elementary School in her car with at least three of her guns, forced his way in by breaking a window and opened fire, authorities said. Within minutes, he killed the children, six adults and himself.

All the victims at the school were shot with a rifle, at least some of them up close, and all were apparently shot more than once, Chief Medical Examiner Dr H Wayne Carver said.

All six adults killed at the school were women. Of the 20 children, eight were boys and 12 were girls.

The tragedy has plunged Newtown into mourning and added the picturesque New England community of 27,000 people to the grim map of towns where mass shootings in recent years have periodically reignited the national debate over gun control.