Backpack, battery, shrapnel at scene
The bomber in the Manchester terrorist attack appears to have carried a powerful explosive in a lightweight metal container concealed within either a black vest or a blue Karrimor backpack, and may have held a small switch in his left hand, according to preliminary information gathered by British authorities.
The initial analysis of the bomb, based on evidence photographed and collected at the crime scene and distributed by British authorities, does not specify the size or type of explosive used in its main charge but suggests an improvised device made with forethought and care.
Law enforcement images of metal nuts and screws propelled by the blast, and of damage nearby, show the bomb’s makeshift shrapnel penetrated metal doors and left deep scuffs in brick walls.
And authorities’ review of the blast site shows that many of the fatalities occurred in a nearly complete circle around the bomber, Salman Abedi, whose upper torso was heaved outside the lethal ring toward the Manchester Arena entrance.
All of t hese are i ndicators of a powerful, high-velocity charge, and of a bomb in which shrapnel was carefully and evenly packed.
One explosive disposal technician who examined the images said the location of the bomber’s torso, and the apparent absence of fatalities in a line between the blast site and where his remains landed, indicated that the explosive charge was more likely in a backpack than in a vest, and propelled the bomber away from the blast.
Certain details of the bomb further suggest a desire by its maker to reduce the risk of a dud.
Authorities found a mangled Yuasa 12-volt, 2.1-amp lead acid battery, which is more powerful than batteries often seen in backpack bombs or suicide vests.
A possible switch to initiate the explosion, carried in the bomber’s left hand, was also unusual in a suicide device in that it appears to have contained a small circuit board soldered inside one end.
It is not clear from the law enforcement images if the object was a simple plunger switch or included a timer or a receiver that could be operated remotely via radio signal — or some combination, or something else.
If the object was the switch, such redundancy could have given the bomber or a terrorist cell more than one option for deploying the device. This suggests that the bomb was not as simple in design as many terrorist devices, which are often crude and prone to failure or haphazard effect.
One independent analyst of improvised explosive devices, Michael Johnson, suggested that the object might be an electronic cigarette and unrelated to the bomb’s detonation — an understandable instance of investigators’ focusing on a crime-scene detail early in a case.
Bomb-disposal technicians who reviewed the images for The New York
Times said a more thorough analysis of the device was difficult without more information, and that assessments of the bomb could change as authorities analyse it further and if they collect more evidence. But its apparent overdesign, including the more powerful than usual battery, could flow from a bomb maker’s difficulty in building a reliable detonator.