James Holmes, the alleged shooter in the massacre in Aurora, Colorado, reportedly amassed his huge arsenal with relative ease. Some of these weapons were illegal as recently as eight years ago. Legislation now before Congress would once again make illegal, if not the guns themselves, at least the high-capacity magazines that allow bullets to be fired rapidly without stopping to reload. Holmes bought most of his weaponry within recent months, we are told. Perhaps, if sane laws on gun control, including the ban on high- capacity magazines, were in place, many in Aurora who are now dead or seriously injured would be alive and well today.

The facts of the assault are generally well-known. Holmes allegedly burst into the packed theater during the 12.30am premier of the Batman sequel "The Dark Knight Rises," threw one or two canisters of some gas or irritant, which exploded, then began to methodically shoot people, killing 12 and wounding 58.

"Everybody sort of started screaming, and that's when the gunman opened fire on the crowd, and pandemonium just broke out," Omar Esparza told me. He was in the third row, with five friends out for a birthday celebration: "He started opening fire on the audience pretty freely, just started shooting in every direction, that's when everybody started screaming, started panicking. A lot of people had been hit at that point at those initial few rounds, and that's when everybody sort of hit the floor and started to exit."

Esparza continued: "It sounded like the bullets had stopped, and it sounded like he was either switching guns or reloading his rifle. At that very second when we sort of heard the silence, we realized that that was our only opportunity of getting out or of dying. So, at that split second, we had to react and had to exit as quickly as possible. And we barely made it, too, because approximately a second after we had exited, we heard him starting to shoot again."

That moment of silence may have been when one of the weapons jammed. CNN reported that "the semiautomatic rifle used in the Colorado theater killings jammed during the rampage ... a law enforcement source with direct knowledge of the investigation said Sunday."

Holmes allegedly had an AR-15, equipped with a 100-round drum magazine, as well as one or two Glock pistols with 40-round extended magazines and a Remington 870 shotgun that can fire up to seven shells without reloading. The AR-15 can fire from 50 to 60 rounds per minute. Holmes had a massive arsenal, easily acquired at retail stores and online.

Carolyn McCarthy is a member of Congress from Long Island, NY. Her husband was shot in the head and among the six killed in the 1993 Long Island Rail Road massacre. Her son also was shot in the head, but survived and remains partially paralyzed. She was a nurse back then, but when her congressman voted against the assault-weapons ban, she ran against him. She won and has been in Congress ever since.

McCarthy has introduced HR 308, the Large Capacity Ammunition Feeding Device Act. It would ban the sale or transfer of these large-capacity clips that enabled the massive casualties in Aurora, and in Tucson, Arizona, in January 2011 when Representative Gabrielle Giffords was shot and six were killed. McCarthy told me: "The problem is, politicians, legislators across this country are intimidated by the NRA and the gun manufacturers who put so much money out there to say that 'we will take you down in an election if you go against us.' Common sense will say we can take prudent gun-safety legislation and try to save people's lives. That is the bottom line."

One group pushing the large-magazine ban is the Brady Campaign to Prevent Gun Violence, named for Jim Brady, who was shot in the head and severely disabled during the 1981 attempted assassination of President Ronald Reagan. I spoke with Colin Goddard, who works for the group. He survived the 2007 Virginia Tech massacre, where 32 people were killed. Goddard was shot four times. I asked him about the refrain so commonly uttered now on television, that it's political opportunism to discuss gun control before the Aurora victims are even buried.

"This conversation should have happened before this shooting in the first place," Goddard replied. "This is when people are outraged. This is when people realize that this could happen to them. We cannot wait ... Now is the time for a change. We are better than this."

• Denis Moynihan contributed research to this column.