The killer: 'Loner' medical student who opened fire and left his nearby flat booby-trapped

The apartment where James Holmes is believed to have planned his attack was the scene of a massive security operation tonight (AP)

James Holmes described himself as “a quiet and easy-going medical student” on the application form he filled out last May before renting a third-floor apartment in a brick-walled building a stone's throw from the University of Colorado's sprawling hospital campus.

Muscular and tall– he measured 6ft 3in – Mr Holmes nonetheless cut an unremarkable figure to neighbours, who largely described him as a "loner". He had moved to Denver from his native San Diego, where he grew up and went to high school, to study for a PHD in neuroscience.

Kaitlyn Fonzi, who rents the flat directly beneath Holmes, told The Independent that she'd never sought to engage with him. But that changed at the stroke of midnight on Thursday, when a stereo in his apartment began playing techno music at high volume, on what sounded like a constant loop.

Ms Fonzi went upstairs to complain, but got no reply when she knocked. "The door looked like it was unlocked but something stopped me from going in," she said.

At exactly 1am, the loud music stopped suddenly, as if it had been on a timer. Almost two hours later, Ms Fonzi discovered that she'd almost certainly had a lucky escape. A police Swat team descended on the building to evacuate residents after being told that the flat had been booby trapped.

Officers peering in its window from a crane spotted "buckets of ammunition" and "some kind of chemical" in the kitchen, beneath a poster of the actor Will Ferrell from the film Anchorman, which was visible on the kitchen wall.

Ms Fonzi, an immunology researcher at the university medical centre, was last night still dressed in her pyjamas. She said entering the upstairs room might have triggered one of the trip wires or pressure pads that were reportedly installed there.

Police said Mr Holmes had neither a criminal record nor ties to terrorist organisations, though his life was believed to be in a state of flux.