Three days after a deadly shooting rampage in a Colorado movie theater, Mayor Michael Bloomberg continued to press the case for tighter gun controls Monday and again offered a pointed challenge to the presidential candidates. YNN's Bobby Cuza filed the following report.

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On Friday, it was 12 dead in a Colorado movie theater. On Sunday, a 4-year-old on a Bronx playground. And on Monday, Mayor Michael Bloomberg again called out President Barack Obama and Republican Mitt Romney for not taking a stand on gun violence.

“Governor Romney signed a bill in Massachusetts prohibiting the sale of assault weapons. And he spoke eloquently about it. Today, he’s not in favor of it. Barack Obama campaigned four years ago on a platform of saying he was going to try to ban the sale of assault weapons. He’s done nothing since then,” Bloomberg said.

While Obama visited Aurora Sunday, both he and Romney have been silent on gun control, a politically divisive topic. The alleged gunman, who was arraigned Monday, purchased his guns legally.

“Even if he didn’t have access to guns, this guy was diabolical, right? He would have found explosives. He would have found something else,” said Colorado Gov. John Hickenlooper.

But Bloomberg, who’s become a leading, national voice on gun control, has continued to beat the drum in TV interviews and at a Q&A with reporters Monday, saying 48,000 people will be killed with illegal guns during the next president’s term.

“People say, ‘Oh well, now’s not the time because we’re mourning,’" he said. "Well, it’s been 16, 18 months since the Arizona massacre and we’ve done nothing. If not now, when?”

Mayor Bloomberg said the debate is not about the Second Amendment but about closing loopholes and rationalizing gun laws so that, for instance, all weapons sales, no matter where they take place, are subject to the same regulations.

Background checks, for example, aren’t required for purchases made at gun shows.

“40 percent of the guns sold in America are sold privately, some at gun shows, which are supposed to be for casual sellers. And in fact you’ll see a dealer with 500 guns at his booth. That’s not a casual seller,” Bloomberg said.

And he wondered whether there should be limits on ammunition, 6,000 rounds of which James Holmes is believed to have bought online.