As investigators raced to figure out who was behind the bombings of the Boston marathon this week, one of the clues was the site itself.
By considering the location of an attack, also known as the "target," experts can gain insight into the motivations of the perpetrators and their level of sophistication.
"It's part of the puzzle when we look at the type of devices used, the pattern of explosions, the materials associated with the explosions, the timing and sequencing of explosions," said Randall Rogan, an expert in crisis negotiation and terrorism at Wake Forest University.
"The biggest indication (of the target) is what the motive was," he added. "This was done to create as much fear and terror and insecurity as possible in the civilian population and to instill a sense of vulnerability."
Experts often refer to two types of targets -- "hard" and "soft." Hard targets are highly patrolled and often symbolic locations, such as military bases, embassies and government buildings. Hard targets are difficult to attack successfully, Rogan said, and hits on them represent an expression of highly organized power and aggressiveness.
Soft targets, on the other hand, refer to unprotected or difficult-to-protect environments that are full of ordinary people -- places like busses, restaurants and sporting events, including marathons. Soft targets are easier to access than hard targets are, and attacks on them more likely to impact the civilian population, both physically and emotionally.
"When you attack a soft target, you're saying, 'You as civilians are not safe anywhere,'" Rogan said. "You are vulnerable at any given point in time."