15 people were killed and more than 20 were injured in Tuesday's Columbine attack

In this story: 'Screaming for national attention' Denver mayor: NRA not wanted RELATED STORIES, SITES

WASHINGTON (CNN) -- One of the major questions surrounding the massacre at Colorado's Columbine High School is how the two teen-age suspects in the attack gained access to so much firepower.

Investigators said sawed-off shotguns, a semi-automatic rifle, a pistol and more than 30 homemade bombs were involved in Tuesday's carnage, which left 15 dead and more than 20 wounded.

Among the dead were the suspects: Eric Harris, 18, and Dylan Klebold, 17, who police said killed themselves after the assault.

Part of the answer to how the two could have been so heavily armed lies in the sheer number of guns in the United States. The FBI estimates that Americans buy 12 million guns every year.

'Screaming for national attention'

Some of those weapons inevitably wind up in the hands of juveniles.

"It's screaming for national attention," said John Magaw, the director of the Bureau of Alcohol, Tobacco and Firearms. "All of us who care about our children in America must come up and address this."

Magaw said there is a number of ways juveniles get guns. Sometimes adults buy guns and then resell them to children. Other times, children simply steal guns that their parents keep at homes.

Information on bomb making, and the necessary ingredients, are even more accessible than guns in the United States, Magaw said.

"There are two or three books on the market that tell you how to make all types of bombs," he said, adding that the Internet is another source for such information.

Denver mayor: NRA not wanted

The shootings at Columbine High School, which is located in a suburban Denver school district, occurred just as the National Rifle Association is preparing to hold a major convention in Denver.

Throughout the city, billboards of actor and NRA group President Charlton Heston holding a rifle promote the NRA event.

While organizers have said they will scale back the NRA convention following the tragedy, Mayor Wellington Webb said it should not be held at all.

"They (the NRA conventioneers) should not come to Denver where they are not wanted," Wellington said. "Given the number of kids that died in the shooting, I think their presence is inappropriate."

He said that "common sense" would dictate that the NRA cancel the event out of respect to the families of the victims.

"What's so bizarre about this," Wellington added, "is for the past three months the Colorado legislature has been trying to abolish all legislation dealing with guns."

Two state legislators were prompted by the shootings to scrap two bills related to gun control issues, one allowing state law to override local ordinances on gun control and another that would have simplified the issuance of permits for concealed weapons.

Wellington said that if the legislators try to revive the gun law debate next year it would be "hypocrisy at its highest level."

Justice Correspondent Pierre Thomas contributed to this report.

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