The scale of an attack can also reveal details about who was behind it, said Anthony C. Roman, CEO of Roman & Associates, a private investigation and security consulting firm in Lynbrook, N.Y.
The 9/11 attacks on the World Trade Center, for example, required significant amounts of planning, large numbers of people engaged in complicated logistics, and a sophisticated command-and-control structure that employed covert communication. The grand goal was to disrupt government, the economy and our daily lives, while also spreading fear. Such an attack had to be the work of a major terror group.
In contrast, Roman said, smaller-scale attacks on soft targets like a marathon can be pulled off with no organizational structure, little money and information about bomb-making pulled off the internet. That leaves open the possibility that a single deranged person planted the bombs in Boston for reasons that are still unclear.
The marathon bomber, in other words, could be the next Timothy McVeigh or Anders Breivik. Equally possible, though, is that a terrorist group wanted to shake things up.
"When you look at the marathon as a soft target and the bombs as reasonably unsophisticated, it can be the work of an individual terrorist sympathizer with no known affiliations, it can be a homegrown domestic terrorist group or it can be a sophisticated international terrorist group that has changed its tactics," Roman said. "It's really difficult to tell at this point."
Though the site of the attack is not enough on its own to reveal who the attackers were, Roman said, the target has factored in to the investigation, along with the materials and methods used to construct the bombs and other evidence, including whether similar attacks follow.
"If we see a pattern," Roman said, "it would be a clue that we have a serious problem."