As people fled Boston’s bloodied marathon route in search of safety on Monday, law enforcement agencies raced in the opposite direction, hoping to find clues pointing to who was behind the deadly attack and why.
They started their search in the double bombing’s gruesome aftermath – amid blood, severed limbs and broken glass.
The Federal Bureau of Investigation is treating Monday’s explosions as a terrorist act.
What they know so far
Two bombs went off in short succession near the finish line of the legendary marathon. There’s evidence the bombs included crude shrapnel meant to extract a high human cost. Three people were killed, including an eight-year-old boy, and more than 170 wounded.
No one has yet claimed responsibility for the bombings, but investigators vowed to “go to the ends of the Earth” to find out who carried out the deadly attack.
They’ll start by scouring the scene itself with a fine tooth comb. In the absence of chatter online or over the airwaves, this is where they’ll look for essential clues, according to former CSIS agent and security expert Michel Juneau-Katsuya.
Searching for a suspect’s ‘signature’
Investigators will start to piece together the chronology of events, searching the site and the victims’ bodies for any remnants of the bomb.
The bombs used in Boston were made of pressure cookers packed with metal and ball bearings and placed in black nylon duffel bags.
“When you’ve collected all those elements, you are capable at that point to be able to find out which materials have been used,” Juneau-Katsuya said.
The way a bomb is constructed can help identify an attacker through markers that one terrorism expert calls “signatures.”
“Telltale signs that could signal who exactly might have been involved in putting these things together – what pieces were involved, what the techniques might have been. Were there quirks of wiring? What about the chemistry involved?” said David Harris with Insignis Strategic Research on the Global News’ The Morning Show.
While the signatures aren’t usually left on purpose, Harris said, they give clues as to who created the bomb, where they learned their methods, and if they have links to any established terrorists organizations. Investigators can also compare this bomb’s attributes to those of explosives elsewhere in the country or the world.
Finding clues in the crowd
Investigating a crime at a major sporting event can be a challenge: For one thing, most people had a backpack, but dropped it and ran after the bomb went off. This forces police to treat each discarded bag as a potential bomb.
But it also gives them a key advantage: thousands of witnesses – many of them taking photos and shooting video of the historic sporting event.
“You put feet on the street and start to pick their memories because the people don’t even know what they remember,” said Chris Mathers, a former RCMP officer who is now a crime and risk consultant. “That’s where you start – good-old fashioned leg work. And then hope.”
Police will pore over photos looking for people carrying black duffel bags. They may also review cell phone traffic and texts made just prior to the detonation.
“Ultimately those videos and photographs will serve to corroborate evidence the police get. They won’t be able to likely to pick the bad guy out of the pictures but once they have the bad guys they’ll be able to go over the pictures,” Mathers said.
Teamwork matters
The police will also have strength in numbers, with thousands likely called in to reinforce the investigative efforts of the Boston police, the FBI and the terrorist taskforce.
“Every detective on the Boston Police will be working on this. Every FBI agent in the greater Boston area will be working on it and they’ll be bringing guys in by the school bus load,” Mathers said.
The FBI is leading the investigation, but the local police will do much of the evidence gathering and questioning on the ground. The process would be similar in Canada, with the RCMP heading up a national investigation assisted by local police forces and CSIS.
“What you want to do is bring everybody to the table that has the expertise in order to be able to gather the evidence, identify the suspect as soon as possible and bring them to justice,” said Ottawa Police Chief Charles Bordeleau .
Mathers believes the investigation will lead American police to a suspect within 72 hours.
“Two people can only keep a secret if one of them is dead,” he said. “Somebody knows about this and eventually every crime gets solved. And one like this certainly does.”
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