The first video footage of the suspect showed him as an awkward, nervous 18-year-old giving a talk at a science summer camp in San Diego on “temporal illusions”. It also emerged that in the days before the attack, Holmes, a cannabis smoker, joined a dating website seeking women for “sexy times” and also tried to join a gun club.

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After the massacre Holmes calmly told detectives he had taken 100mg of the prescription painkiller Vicodin, and identified himself as “The Joker”. The same drug was found in the system of actor Heath Ledger when he died of an accidental overdose of prescription drugs in 2008. Ledger played The Joker in the previous Batman film The Dark Knight. Vicodin side-effects can include euphoria, paranoia and, in rare cases, hallucinations.

The video footage of Holmes was taken at Miramar College in San Diego and showed him explaining that “temporal illusions” are “an illusion that allows you to change the past”. Holmes said he had been working on “subjective experience, which is what takes place inside the mind as oppose to the external world”.