(Ed Andrieski/AP Photo)

The worst mass shooting in U.S. history has sparked a renewed debate about gun control laws in the country.

James Holmes, a 24 year old student at the University of Colorado Medical School was detained Friday following the shooting of 70 people inside a movie theater in Aurora, Colo. Twelve people were killed in the attack, which was carried out with an assault rifle, a shotgun and a pair of Glock pistols at the midnight screening of "The Dark Knight Rises."

Not much is yet known about Holmes, but investigations into the weapons he owns show that he purchased them legally. He purchased the four guns at local shops, and bought more than 6,000 rounds of ammunition on the Internet in the past 60 days, Aurora Police Chief Dan Oates said.

"All the ammunition he possessed, he possessed legally, all the weapons he possessed, he possessed legally, all the clips he possessed, he possessed legally," Oates said. As far as investigators know now, Holmes had a clean background, with the exception of a single traffic ticket.

The right to bear arms is a constitutionally protected right in America, and in Colorado, the laws aren't very strict. Background checks are required for purchases at gun shows, under an initiative voted into law after the Columbine shootings in 2000. However, there is no ban on assault weapons or high capacity ammunition clips. Registration and gun owner licenses aren't required, and background checks for online sales aren't required.

Advocates of increased gun control laws point to events like this one as evidence that the nation needs to adopt stricter laws about who can buy firearms, and what firearms they can buy.

New York City Mayor Bloomberg has been an outspoken advocate of stronger gun control rules as a chair of Mayors Against Illegal Guns. On his radio show Friday, Bloomberg called on top politicians to make their stance on gun laws clear.

"Maybe it's time that the two people who want to be president of the United States stand up and tell us what they're going to do," Bloomberg said. "Because this is obviously a problem across the country."

Polls indicate most Americans favor stricter gun laws, but the issue hasn't been rated as a highly important political one, because of conflicting sentiments about how to respond. Many people think stricter enforcement of existing laws is preferable to creating new laws, and that the availability of guns is not itself the primary cause of gun violence.

In the past, attitudes toward gun laws haven't changed in response to gun crimes like the Aurora movie theater shooting.

Still, gun sales are climbing, and few politicians are willing to work towards strengthening gun laws.

This debate isn't a new one for the community surrounding Aurora. Columbine, where 13 years ago two students opened fire on their high school classmates, killing 13, is just a short drive from Aurora.

Tom Mauser, whose son Daniel was killed at Columbine, became a gun control advocate following his son's death.

"It makes me angry. It makes me angry for America when other countries are looking at us saying, 'are you nuts?'" Mauser told ABC News' Clayton Sandell. "When you have magazines that can hold 30, 50, 100 rounds, that makes it easy for people like [the Aurora movie theater shooter]."

According to the latest numbers of the Bureau of Alcohol, Tobacco and Firearms, there are 123,000 licensed firearms dealers in the United States, meaning there are roughly as many gun dealers as there are gas stations.

Between 2006 and 2010 more than 47,000 people were killed in the United States by firearms, according to ATF reports.

Pro-gun rights advocates argue that gun ownership is a protected right, and that law-abiding gun owners shouldn't be punished because of those who break the law.

"You can't stop selling guns. If you're going to be in an armed country, you're just going to have to deal with the occasional fruit loop," gun owner Andrew Wright told Sandell. "That's the way it goes. It's unfortunate, it really is."