Among the weapons officials have said were in the possession of Tamerlan and Dzhokhar Tsarnaev were not only several bombs, but handguns, an M-4 carbine rifle and more than 250 rounds of ammunition.
Much of that arsenal was on fiery display when the brothers engaged in a wild gun battle with police in suburban Watertown early Friday, shortly after images of them milling about the marathon's finish line were released to the public by the FBI.
Tamerlan Tsarnaev, 26, died following that gun battle while a Boston transit police officer was gravely wounded. The Tsarnaev brothers are also the prime suspects in the execution-style shooting of a security officer at the Massachusetts Institute of Technology a couple of hours before the gun battle.
"There was a lot of firepower employed," White House press secretary Jay Carney told the daily news briefing on Monday.
"But beyond that, which is information that's obvious to anyone who was paying attention, I'm not going to characterize ... what weapons may or may not have been recovered."
Carney added that President Barack Obama is determined to push through "common-sense measures and make them law to reduce gun violence in America" despite the defeat of his proposals last week.
Neither Tsarnaev brother had licences to carry firearms, police say.
But even if they'd wanted to acquire the weapons legally — unlikely, considering they were allegedly plotting a terrorist attack — they could have obtained them without submitting to a background check under current laws.
Tougher background checks likely would have caused problems for Tamerlan Tsarnaev, who died following the shootout, given his past brushes with authorities.
Tsarnaev's father, Aznor, said from Russia last week that his eldest son was denied U.S. citizenship because he'd been charged with domestic assault after he was accused of hitting his American girlfriend three years ago.
The FBI also had Tsarnaev on their radar as someone Russia suspected had links to terrorists, something that might also have tripped him up if he'd legally attempted to purchase firearms from a licensed dealer.
Last week, the U.S. Senate voted against modest gun control proposals that would have expanded and strengthened background checks for firearms purchases. Under current law, Americans wishing to obtain guns need to have a background check for certain types of purchases — such as from a licensed dealer — but aren't subjected to them if they buy them elsewhere, including at gun shows or on the Internet.
Police aren't certain how or where the bombing suspects obtained such an array of expensive weaponry.
Tsarnaev's younger brother, Dzhokhar, 19, was charged in the bombings on Monday as he lay in a Boston hospital bed recovering from gunshot wounds, including a neck injury believed to be self-inflicted and the result of a failed suicide attempt.
The 19-year-old college student is charged with conspiring to use weapons of mass destruction against persons and property in the U.S. resulting in death. He faces a death sentence.
The White House announced earlier Monday that the teen would not be deemed an enemy combatant — a classification some Republican lawmakers had pushed for. As a U.S. citizen, the younger Tsarnaev brother will be tried in a civilian court.
"We will prosecute this terrorist through our civilian system of justice," Carney said.
He added it was illegal to try an American citizen in a military commission, pointing out that several high-profile terrorism cases have been handled in civilian courts. That includes the trial of the so-called underwear bomber, who was convicted of trying to bring down a passenger jet in late 2009 by detonating explosives in his undergarments.
The debate about how to handle accused terrorists is now dovetailing with the ongoing national debate about gun control. Not surprisingly, both sides on the argument are pointing to the Boston Marathon bombings to bolster their case.
Gun control advocates are expressing alarm at how easily the suspects were apparently able to acquire powerful weaponry, possibly without even breaking any laws if they obtained them at gun shows.
"The bombs are a reach from the gun legislation, but they did have guns," Patricia Maich, a survivor of 2011's mass shooting in Tucson, Ariz., said Monday.
"I don't know if they were illegal or legal. But we are not Pollyannas. We know that not every gun violence issue and incident will be stopped by a background check. But it certainly will stop some."
Those opposed to gun control, on the other hand, say the Boston bombings prove that gun laws don't work.
"Last week's events simply do not bring the national debate on gun control laws back into the picture. If anything, the Tsarnaev brothers have highlighted why gun control laws don't work," wrote Jason Pye on the right-wing United Liberty website.
"No matter how restrictive gun laws are, criminals will still obtain firearms. They don't care about the restrictions or background checks. These two guys were set on killing people in whatever manner they could, no law was going to prevent that."
A majority of the Senate supported the legislation to strengthen background checks, but it failed to get the 60 votes needed to move ahead. Polls suggest 90 per cent of Americans, including gun owners and Republicans, support tougher background checks.
Obama accused the powerful National Rifle Association of lying to the public about gun control while he lambasted the Senate last week for failing to pass new laws on background checks. The NRA contributes funding to many lawmakers, and warned it would hold them accountable if they voted for the president's gun control proposals.
The NRA even opposes legislation banning gun sales to people on the existing terrorist watchlist, however. The organization argues that the watchlist is arbitrary and has no due process behind it.
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