Gunman kills twelve at Batman screening

The United States was rocked by one of its worst mass shootings when a man opened fire at a midnight screening of the Batman film 'The Dark Knight Rises'.

Wearing a gas mask and dressed in full body armour, 24-year-old ex-neuroscience student James Holmes threw tear gas canisters into the cinema before firing at random into a packed auditorium with a high-powered assault rifle.

Twelve people died at the scene, with another 58 left wounded.

Holmes reportedly entered the cinema via an emergency exit door near the front of the cinema.

Witnesses described the horror of the attack saying the gunman had "slowly made his way up the stairs just firing – picking random people."

The university dropout gave himself up to police outside the cinema, reportedly still wearing his body armour.

Holmes allegedly told police he was 'The Joker', Batman's sworn enemy in the movie franchise.

High-profile celebrities took to Twitter to condemn the attacks, including the star of the Batman film, Christian Bale.

"I cannot begin to truly understand the pain and grief of the victims and their loved ones, but my heart goes out to them," he wrote.

The director of the movie, Chris Nolan, also released a statement expressing his grief.

"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," he wrote.

"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."

Both Christian Bale and President Barack Obama visited victims of the shooting in Colorado and thanked medical staff and police for their response.

Tragic acts of bravery emerged from the shooting with two men making the ultimate sacrifice to protect their girlfriends.

Alexander Teves, 24, lunged on top of his girlfriend Amanda Lindgren to block her from the gunfire.

“He held me down, and he covered my head and he said 'Shh just stay down'. So I did," Lindgren said. She was unharmed, but Teves received multiple gunshot wounds and died at the scene.

A six-year-old girl and a man celebrating his 27th birthday were among the other victims.

Police and bomb technicians spent nearly two days at Holmes's apartment following the mass shooting, after sophisticated booby traps were discovered.

Law enforcement officials say more than 30 devices were disarmed, including threats containing a kind of homemade napalm and other accelerants in bottles that would have destroyed the apartment.

Described by those who knew him as a highly-intelligent student and former camp counsellor, Holmes was also somewhat of a loner who was reportedly rarely seen in social settings.

A motive for the crime is still unclear, however multiple sources have cited the fact that Holmes had failed an important oral exam and was in the process of withdrawing from a doctoral program at the University of Colorado-Denver.

The accused gunman allegedly bought a high-powered rifle hours after failing the test, and in the lead up to the shooting stocked up on more than 6000 rounds of ammunition. He also bought four weapons from local gun shops.

Reports also emerged that Holmes had sent a package to his psychiatrist prior to the shooting that included drawings of a stick-figure gunman killing multiple people.

Holmes's first appearance in court garnered worldwide attention. With orange-dyed hair, the 24-year-old looked wild-eyed and confused, sparking speculation about his mental state.

On the July 31 Holmes was charged with two counts of first degree murder for each of the twelve people killed. He is also facing 116 attempted murder charges for endangering the lives of all people within the cinema.

At this stage, he is yet to enter a plea, but it is believed that his defence team will plead not guilty on grounds of insanity.

In mid-November, the accused mass killer attempted to harm himself by running head-first into a prison cell wall. He was hospitalised for a short period, however according to reports he was not seriously hurt and was later released.