Boston Marathon bombing: what the suspects' arsenal reveals

The quality and quantity of the Boston bombing suspects' armaments suggest a future attack was planned, but don't answer the question of whether they had outside help.

The alleged Boston Marathon bombers had an arsenal of weapons that went beyond the explosive devices used at the marathon – and which could have been intended for use in subsequent terror attacks.

That’s the picture that has been emerging from law enforcement officials one week after the deadly attack at Boston’s marathon finish line.

A criminal complaint against Dzhokhar Tsarnaev, filed Monday as he was being cared for at a Boston hospital, allege that he and his brother, now dead, wielded guns and numerous explosives as they were being pursued by police days after the initial bomb attacks.

"We have reason to believe, based upon the evidence that was found at that scene – the explosions, the explosive ordnance that was unexploded and the firepower that they had – that they were going to attack other individuals," Boston Police Commissioner Edward Davis said in an interview on CBS News Sunday. "That's my belief at this point.”

The brothers allegedly used handguns and a rifle during their confrontation with police, but had no firearms registered with local authorities. The New York Times identified the rifle as an M-4 carbine, a weapon capable of firing in multi-bullet bursts.  

The Tsarnaev brothers also threw or dropped explosive devices, apparently loaded from their Cambridge, Mass., apartment into a hijacked car, Commissioner Davis said. The devices caused "one extremely loud explosion” and several others, he said.

Some news reports have also said the suspects made pipe bombs, although those were not mentioned in the criminal complaint against the surviving brother, filed Monday by FBI Special Agent Daniel Genck in US District Court in Massachusetts.

The substantial arsenal doesn’t answer the question of whether the perpetrators acted alone or had aid or instruction from others. Terrorism experts have expressed mixed views on that question.

Some have criticized Boston Mayor Thomas Menino for publicizing the idea that the brothers probably acted alone, while others have embraced that same idea – saying the deeds could be done on their own even if there was one or more additional individual who influenced the “radicalization” of thought that led to the attacks.

Special Agent Genck described the marathon-day devices as “low-grade” explosives housed in pressure cookers. He says a device deployed at the scene of a shootout with the Tsarnaevs later last week in the Boston suburb of Watertown used the same brand of pressure cooker and the same kind of green hobby fuse.

Some terrorism experts say the know-how to make such explosive devices is obtainable on the Internet, while others say it's likely that some training was behind the building of these improvised explosive devices (IEDs). Investigators have recovered at least two unexploded devices from the shootout scene, as well as pieces of exploded devices, to analyze.

Davis of the Boston Police said the federal officials are now trying to trace where the firearms used in the gun battle came from.

The shootout has brought out familiar views on gun control. Gun-rights proponents argue that criminals will always circumvent restrictions. But proponents say a tighter system of oversight on gun purchases would make these weapons harder to acquire and impose greater accountability on those who sell guns.