James Eagan Holmes, the man suspected of shooting dead 12 people in a cinema in a Denver suburb, applied to join a local gun range last month, but the "freakish" greeting on his voicemail made the club owner decide to turn him away.
The revelation will help police trying to piece together the detailed planning that went into the massacre and into the preparation of a booby-trap bomb at the suspect's apartment that was designed to cause a second scene of mayhem.
Holmes himself has "lawyered up" and is not co-operating with the authorities, the local police chief said last night, as President Barack Obama swept into Aurora to meet with victims and their families and offer words of condolence to a grieving town.
Holmes emailed an application to join the Lead Valley Range in Byers on 25 June, according to the club owner Glenn Rotkovich. When Mr Rotkovich called to invite him to a mandatory orientation the following week, he said he heard a message on Holmes's voicemail that was "bizarre – guttural, freakish at best". After leaving two other messages, he eventually told his staff to watch out for Holmes at the orientation and not to accept him into the club.
Meanwhile, the 24-year-old may have used his position as a researcher at the University of Colorado to order the equipment for a bomb, it has emerged.
The university said it was investigating what might have been in packages that were sent to Holmes at the neuroscience research lab at its medical school. Holmes was in the process of dropping out of the PhD programme when he is alleged to have gone on the worst gun rampage in US history, in terms of numbers killed or injured. Aurora police said that Holmes received 50 commercial packages at his home and school addresses in the four months leading up to his rampage – "evidence of a deliberative process to commit this assault and a deliberative process to attack whoever walked through the door of that apartment", Aurora Police Chief Daniel Oates said.
Holmes is due to make his first court appearance this morning. He is being held in solitary confinement at a Denver-area county detention facility.
A CV posted online shows Holmes had mapped the neurons of Zebra finches and studied the flight muscles of hummingbirds while an undergraduate at the University of California, Riverside. But neighbours and former classmates in California said although he was smart, he was a loner who said little and was easily forgotten. It is not clear why he was withdrawing from his PhD programme, or whether he had passed an intense oral exam to mark the end of the first year.
Mr Obama spent the afternoon in Aurora for private meetings with families of the dead and survivors, and with local officials and emergency service workers. The community was also planning to come together for a memorial service and vigil near the site of the massacre.
The heartbreaking stories of the dead and injured range from the mother who spent days fighting for her life in hospital, then to be told that her six-year-old was killed in the cinema, to the workers of a nearby restaurant, which had eight of their number injured at the screening – one of them fatally. The full list of the victims was published late on Sunday, their ages ranging from six to 51.
The gun-range owner told his staff to watch out for Holmes and not accept his application to join the club