Pressure cookers help make good bombs _ and clues

 

 

Pressure cookers help make good bombs _ and clues

By SETH BORENSTEIN

- Apr. 16 8:52 PM EDT

http://bigstory.ap.org/article/pressure-cookers-help-make-good-bombs-and-clues

 

 

 

WASHINGTON (AP) - In kitchens, they prepare food faster, but pressure

cookers by their very nature help make good bombs, amplifying the blast and

the carnage.

 

They don't just hold the explosives. The tightly sealed pot that speeds the

cooking of beans and meat makes easier-to-obtain but weaker explosives

faster and stronger. And they may also help investigators find out who built

the deadly homemade bombs that exploded at the Boston Marathon on Monday.

 

Investigators found fragments of BBs and nails, possibly contained in a

pressure cooker, said Richard DesLauriers, the FBI agent in charge in

Boston. He said the items were sent for analysis.

 

If a pressure cooker was used, it probably cost around $100 to construct,

say former federal forensic and explosive investigators. It's like a pipe

bomb but bigger and more powerful.

 

Pressure cooker bombs are more often used in Afghanistan, Pakistan India,

and Nepal - where the pots are more commonly used for cooking. But they have

also been prominent in bombings and attempts in the United States,

especially in New York in Times Square in 2010 and Grand Central Terminal in

1976.

 

In Al Qaeda's online magazine, there's even an article titled: "Make a bomb

in the kitchen of your mom" by "The AQ Chef." It mentions, even recommends,

pressure cookers, noting that weak explosives only work with the high

pressure of a cooker or sealed pipe.

 

Low power explosives like black powder and smokeless powder - the most

likely ones used in Boston - blow up at a slower rate and only deliver the

big boom if they are confined and the pressure from the gas and explosion

builds up, said Denny Kline, a former FBI explosives expert and instructor

in forensics at its academy.

 

Kline and other ex-government experts who have no role in the investigation

differ about what type of explosive may have been used and some refuse to

even speculate what kind.

 

The pressure cookers are a key first piece in a painstaking detective

process. The sound of the explosion is a clue. The color of the flash -

yellow - and smoke - white - are clues. So is the size of any crater and the

distance fragments flew. Even the smell can give a seasoned investigator a

good idea of what explosive was used, Kline said.

 

"We basically try to create a model for what the bomb looked like," said

Matthew Horace, a former special agent for the Bureau of Alcohol Tobacco,

Firearms and Explosives. "Investigating bombs is like a puzzle."

 

Piece by piece, forensic investigators now have to put together what came

apart with an explosive force of thousands of feet per second: The bombs

themselves.

 

"It's going to change its appearance and its form, but it's going to

remain," said Kline. "It'll be broken up into lots of little pieces, but

it's not going to evaporate."

 

The job is to piece things back together and identify chemicals. But it

happens slower than on TV crime shows. And it isn't as easy, Kline said.

 

"It takes a lot more intelligence to put it back together... from multiple

pieces than to follow a simple set of instructions on the Internet," said

Roy Parker, a retired ATF explosives expert.

 

Kline said once forensic investigators have something on the bomb itself, it

is given to lead detectives to take the next big step

 

Take the pressure cooker. If the brand is determined, "investigators will

track every store that sells that pressure cooker and when it was built and

sold," Horace said. "This kind of investigation requires hundreds, if not

thousands of leads to be followed up on."

 

Horace and others are confident that the pressure cooker identification can

be a big help.

 

The pressure cooker can also help point to the type of explosive, Kline

said. If it's a high powered explosive like dynamite or C4, the blast would

have shattered the cooker leaving sharp edges. If it's the low explosive, it

will merely blast through, leaving more squared off edges, he said.

 

Once everything is pieced together, investigators will look for the

"signature" or style of a bomber. Often - but less so since the Internet was

born - a signature can lead to a bomber, Kline said.

 

"It's like a piano player," Kline said. "You can give Dave Brubeck or Chopin

the same piece of music and it will sound different."

 

With this type of bomb, it can be triggered with something as simple as an

egg timer or alarm clock, Parker said. Experts doubt a cellphone was used.

 

The use of nails, shards of metals and ball bearings also amplifies the

personal devastation, experts said.

 

"We've removed BBs and we've removed nails from kids. One of the sickest

things for me was just to see nails sticking out of a little girl's body,"

said Dr. David Mooney, trauma chief at Boston Children's Hospital, which

treated 10 blast victims.

 

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