Rifle in Colorado attack jammed: Cops

Attack calculated,gunman got arm deliveries for 4 months at university

The semiautomatic assault rifle used by the gunman in a mass shooting at a midnight showing of the latest Batman movie jammed during the attack,a federal law enforcement official said,which forced the shooter to switch to another gun with less fire power.

The official,who spoke on condition of anonymity,said the disabled weapon had a high-capacity ammunition magazine. Police have said that a 100-round drum magazine was recovered at the scene and that such a device would be able to fire 50 to 60 rounds a minute.

That account of what happened inside the Century 16 theatre emerged with other details of a suspect described as a budding scientist,brimming with potential,who pursued a graduate programme even as he planned the attack with calculation and deliberation, police said Saturday.

James Holmes,24,received shipments that authorities believe armed him for battle and were used to booby trap his home with dozens of bombs.

He got several mail deliveries over four months to his home and school and bought thousands rounds of ammunition on the Internet.

In Aurora,investigators spent hours Saturday removing explosive materials from inside Holmes apartment a day after police said he opened fire and set off gas canisters in a theatre minutes into a premiere of the The Dark Knight Rises. The massacre left 12 people dead and 58 injured.

His apartment was rigged with jars of liquids,explosives and chemicals that were booby trapped to kill whoever entered it, Aurora Police Chief Dan Oates said,noting it would have likely been one of his officers.

Suspects profile

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Holmes had recently withdrawn from a graduate programme in neuroscience at the University of Colorado Denver. He was one of six to get the National Institutes of Health grant money.

The university said Holmes gave no reason for his withdrawal,a decision he made in June.

A resume of Holmes paints a picture of a brilliant young man: He mapped the neurons of Zebra finches and studied the flight muscles of hummingbirds at the University of California,Riverside.

He worked as a cabin counselor to underprivileged children at a summer camp in Los Angeles in 2008.

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Neighbours and former classmates in California said although Holmes was smart,he was a loner who said little.