US begin to mourn the 12 people killed by a gunman at a showing of the new Batman film, The Dark Knight Rises, and a candlelit vigil has been held in Aurora, Colorado.

US President Barack Obama ordered flags flown at half mast.

A man in a gas mask and body armour threw tear gas canisters at a midnight screening, then fired on the crowd, killing 12 and injuring 58.

Suspect James Holmes, 24, was arrested outside the cinema, police said.

He will appear at Arapahoe County District Court, in nearby Centennial, Colorado, on Monday at 09:30 local time.

Hundreds of mourners gathered in Aurora for the vigil.

Candles and flowers were left on the lawn. One letter read: “To all the innocent souls… This is for you. We will never forget. This is Aurora.”

At the Queen of Peace Roman Catholic church, Denver Archbishop Samuel Aquila told mourners: “Blessed are those who mourn, for they will be comforted. The heart of our Father is stronger than the bullets that killed 12 people.”

In a briefing at the end of the day in Colorado, an emotional Governor John Hickenlooper confirmed that the casualty figure had been revised down one, to 70 people killed or injured.

Thirty people remained in hospital, John Hickenlooper said, with 11 of those in a critical condition.

“It’s an act that defies description. Everyone I’ve talked to all day is filled with an anger that can’t find focus,” he said.

Aurora police chief Dan Oates said the attempt to defuse complex booby-traps, explosive devices and “things that look like mortar rounds” at James Holmes’s home had been abandoned for the night, with federal government experts due to arrive on Saturday.

“I’ve personally never seen anything like what we’ve found in there,” the police chief said.

Suspect James Holmes, 24, was arrested outside the cinema

James Holmes was said to be armed with a rifle, a shotgun and two pistols when he launched his assault. All weapons and ammunition were bought legally within the past few months, Dan Oates said.

Authorities have established no terrorism link, nor any motive, and James Holmes had no criminal record in Aurora.

In New York, Police Commissioner Raymond Kelly said the suspect had dyed his hair red and told police he was the Joker, Batman‘s infamous nemesis.

Cinemas in that city tightened security at Batman showings following the attack, and the French premiere of the film in Paris was cancelled.

The film’s director, Christopher Nolan, issued a statement expressing his horror.

“The movie theatre is my home, and the idea that someone would violate that innocent and hopeful place in such an unbearably savage way is devastating to me,” Christopher Nolan said.

“Nothing any of us can say could ever adequately express our feelings for the innocent victims of this appalling crime, but our thoughts are with them and their families.”

Despite a strong past academic record, James Holmes was in the process of withdrawing from a doctoral programme in neuroscience at the University of Colorado-Denver.

One neighbor told Agence France-Presse that James Holmes “was always wearing camouflage pants”, adding: “We did not know him well because he talked to nobody. He was always locked up behind his door.”

His family said in a written statement: “Our hearts go out to those who were involved in this tragedy and to the families and friends of those involved. We ask that the media respect our privacy during this difficult time.”

Police have given no indication of the names of the dead, the last of whose bodies was removed from the cinema at about 17:00 on Friday.

One woman known to have been killed was Jessica Ghawi, also known as Jessica Redfield, an aspiring broadcaster and a regular blogger.

In June, Jessica Ghawi, 24, narrowly missed being caught in a shooting rampage in Toronto, leaving the scene five minutes before a man opened fire at the Eaton Centre shopping mall.

The attack began minutes into the showing at about 00:30 local time, when the gunman apparently entered the cinema through an emergency exit door near the front of the auditorium.

Reports said the attacker had a ticket but left the cinema, pretending to receive a phone call, before returning fully armed.

He wore a bullet-proof vest, tactical body armor and gloves, and was carrying an AR-15 military-style, semi-automatic rifle, a shotgun and two pistols, police said.

He threw two tear gas grenades, then opened fire with a rifle. There was chaos as movie-goers fled, some dressed in costume as heroes and villains.

Ten people were killed at the cinema and two others died later in hospital of their wounds. Among the injured were a four-month-old baby, who was released from hospital after treatment, and a six-year-old child.

One witness said the gunman had been “slowly making his way up the stairs and just firing – picking random people”. At least one person in an adjacent auditorium was injured when a bullet went through the wall, police said.

Another eyewitness, identified only as Pam, said: “He fired a canister into the air. It shot right into the air, then I started to hear the bang, bang, bang of a gun.”

Salina Jordan, 19, told the Denver Post she had seen one girl shot in the cheek, and a girl who appeared to be about nine years old with a gunshot wound to the stomach.

Informed of the massacre at dawn, President Barack Obama spoke briefly to a campaign rally before returning to the White House to address the situation.

“There are going to be other days for politics,” he said.

“This, I think, is a day for prayer and reflection.”

Cinema shooting suspect:

• James Holmes, 24, was a former neuroscience PhD student at University of Colorado-Denver

• Attended high school in San Diego, California, where his parents still live

• He lived in an apartment in north of Aurora, about five miles from the cinema

• Only previous brush with the law was a summons for speeding in October 2011

Colorado gun laws:

• Residents allowed to keep guns in homes, offices and vehicles, but can only carry them in public with a permit

• There are no limits to how many guns can be bought a month, and the state permits sale of automatic weapons

• No waiting period for buying a handgun, both state and federal state law requires criminal background checks

• Since 1998 Columbine massacre, 20 miles from scene of Friday’s shooting, it has become easier to buy guns in US – a national ban on assault weapons sale expired in 2004