Open source networks are stating that the explosive devices have killed 3 people, with more than 140 people wounded and receiving varying degrees of medical attention. The death toll could rise as 8 wounded people are listed by authorities as being in critical condition.
Close to the time of the explosion an individual had unsuccessfully attempted to gain access to a restricted area near the finish line. Film footage of the attack shows that the explosion occurred at the base of a building, which would deflect most of the blast away from the building and into the crowd. Reports indicate that the explosives were constructed with gunpowder, ball bearings, and other shrapnel material to cause maximum damage, injury, and death.
Additional information provided indicates that the targets were the runners themselves, which would be a possibility if the individual who tried to gain access to the restricted area was the perpetrator of the attack. The intended target could also have been the audience, as film footage shows that the seat of the explosion was behind the crowd. There are also reports of two other devices being disarmed with no current indication where these devices may have been planted.
This attack was likely planned with great detail, and it is possible that reconnaissance of the race was conducted by the attackers at a previous year's Boston Marathon. The Boston Marathon is a long-standing public event, which would have facilitated reconnaissance of it. It is also possible that the explosive devices were planted inside a building next to a window, which would emphasize the shrapnel damage, however, there are no reports to indicate this, and the seat of the explosion appeared next to a wall.
The second explosion may have detonated prematurely, and could have been designed as a secondary device which would have caught other people as they fled the initial blast. This tactic would have been similar to that deployed during the bombing of a popular tourist site in Bali, Indonesia in October 2012. Reports of two other possible explosive devices may have only been suspicious objects that have been "defused," as authorities and the public near the site of the attack would have been understandably apprehensive about any suspicious objects after the bombing.
Also, the person or people responsible for this attack are most likely what are classified as "Lone Wolves" that are acting on their own without an organization's direction. Lone Wolves can, however, share an ideology with other militant organizations and act individually out of a desire to further an objective that they share with a larger network of people. Militant jihadists, for example, may not be part of al-Qaeda but are influenced by the work of the jihadist "theorist" Abu Musab al-Souri who advocated the waging of fard al 'ayn (individual jihad without structures or organization to hamper the effort) attacks. Some reports also indicate that the attacker could be from the "far right", however, attackers of this ideological persuasion would target a particular audience that they hate, such as Jewish, gay, or black people. This attack does not indicate targeting of this type.
It is likely that an individual or group linked to al-Qaeda will attempt to take credit for this attack. There is a possibility that the attack was conducted by a person or organization that held a grudge against some specific person, group, or circumstance of the event. This is unlikely, however, due to what appears to be a large amount of planning in the targeting and execution of the bombing.
Paul Ashley is the Senior Counter-Terrorist Analyst at 361 Security