The alleged Colorado gunman legally purchased four guns, including a military-style assault rifle and a special magazine that meant he could fire off 50 to 60 deadly bullets a minute.
Over eight weeks he stocked up over the Internet on 6,300 rounds of ammunition: 3,000 for his .233 semi-automatic AR-15 rifle, another 3,000 for his two .22 Glocks, and 300 cartridges for his pump-action shotgun.
When the gun dealers performed the minimal background checks required under Colorado law, no alarm bells went off because all 24-year-old James Holmes had against his name was a speeding ticket, officials said.
On Friday, the gunman entered the midnight premiere of the latest Batman movie, The Dark Knight Rises, and sprayed bullets into the packed cinema, killing 12 people and wounding 58 others in a matter of minutes.
The Aurora massacre joins the litany of horrific US shooting incidents that include Columbine High School (13 killed in 1999), Virginia Tech (32 killed in 2007), and last year's shooting in Tucson, Arizona that killed six people and left congresswoman Gabby Giffords fighting for her life.
Gun control advocates believe America is more prone to mass shootings than other countries because it has lax gun laws in many states.
"Somebody's got to do something about this," New York Mayor Michael Bloomberg, who is calling for more stringent background checks on gun-buyers, told CBS's Face the Nation program.
Senator Frank Lautenberg, a Democrat from New Jersey who plans to reintroduce legislation that would curtail the ability of a shooter to fire repeatedly without reloading, agreed.
"We have to face the reality that these types of tragedies will continue to occur unless we do something about our nation's lax gun laws," he said.
Despite profound soul-searching over America's latest rampage, no one sees any willingness on either side of the political aisle to tackle the long stalemate over the toxic guns issue, especially in an election year.
Several key battlegrounds in November's election -- Ohio, Pennsylvania and Virginia, for example -- have gun-friendly populations that remain wedded to the "right to bear arms" enshrined in the US constitution.
The gun lobby, led by the National Rifle Association (NRA), is well-funded and a powerful player in Washington. It argues that crazy people do crazy things and says clamping down on fundamental American liberties will achieve nothing.
Colorado Governor John Hickenlooper said Holmes was clearly a "very intelligent individual" who knew how to make bombs and would have found other ways to kill.
"He would have found explosives, he would have found something else, some sort of poisonous gas, he would have done something to create this horror," Hickenlooper, a Democrat, told ABC's This Week program.
As Republican Senator John McCain pointed out -- coincidentally on the first anniversary of the massacre of 77 people in Norway by a right-wing extremist -- horrific shootings can happen anywhere.
"The killer in Norway was in a country that had very strict gun control laws and yet he was still able to acquire the necessary means to initiate and carry out a mass slaughter," McCain told CNN's State of the Union program.
Gun control advocates recoil from such logic and say that regardless it would make sense to ban assault weapons and large capacity magazines, and to strengthen laws to make sure more red flags show up when certain people try to purchase weapons.
