The explosions at the Boston Marathon on Monday were likely caused by high-power black powder explosives, bomb experts tell U.S. News, and at least one of them was likely shaped in a pipe bomb.
Footage of the initial detonation of the blast showed an explosive plume that would align with a high-powered pipe bomb, says Fred Burton, a retired Diplomatic Security Service special agent who helped investigate the first World Trade Center bombing, among other high-profile attacks.
"This will rewrite the rules for large event management," says Burton, now the vice president for intelligence at private security firm Stratfor. "This is going to raise all kinds of questions regarding how you screen spectators and visitors and personnel for these large public events."
The City of Boston is primarily responsible for containing the crime scene, he says. Those EMS and police officers will soon be joined by an FBI Joint Terrorism Task Force who will work with local officials to oversee the scene.
Ed Davis, the Boston Police commissioner, said Monday afternoon he has contacted the FBI special agent in charge to begin coordinating the investigation.
"It's a brilliant soft target kind of location to try to strike," says Burton. "You're going to have crowds. You're going to have noise, and the chaos of cooking off one of these devices."
The Boston Marathon already draws international media coverage, involves a "tremendous amount of international runners" and is "a very high profile event that's televised," he says.
Building a pipe bomb does not require a great degree of sophistication, Burton says, but getting them to function properly "does take some practice."
Reports of "traumatic amputations" among the victims of the explosions indicate this was likely very powerful explosive device, says Paul Fennewald, a 23-year veteran of the FBI as a bomb technician.
The white smoke that emanated from the blasts indicate this was likely a smokeless or black powder, he says, not a military-type explosive such as C-4 or plastic explosives, which give off black smoke. Two explosions in quick succession also indicate this was likely a terrorist attack.
Al-Qaida and other radical Islamist groups don't often choose significant or historic dates for their attacks, says Fennewald, who also served as the Missouri Homeland Security Coordinator.
"They do their bombings whenever they're ready to do them," he says.
Monday's explosion occurred on Massachusetts's Patriots Day, indicating a domestic terrorist group could be responsible, if the explosions were indeed a terrorist attack.
Investigators are likely looking for what detonated the explosion, such as a radio device or a timer, and when it was placed amid ongoing security sweeps of the area. That information will yield much more about the character of the potential attacker.
Both experts look to the international character of the Boston Marathon, which draws runners from throughout the world to compete. A terrorist attack at the event might be designed to send a signal, or it could be targeting one particular runner, says Fennewald.