Detectives Read Fragments To Identify Bombs

April 30, 1995|By DAVID FISHER

It is the bomb, more than any other weapon, that makes you vulnerable. Unlike a firearm, a bomb doesn't have to be aimed. Unlike poison, it doesn't have to be administered. The bomber doesn't have to be near you. Bombs are weapons of chance as much as choice; the victims are simply in the wrong place at the wrong time. Bombs kill randomly, making them the perfect terror weapon, and they have changed the way we live.

The size of a bomb is much less important than its placement. A bomb that weighed no more than 14 ounces and was concealed inside a portable radio killed more than 271 people when it blew apart Pan Am Flight 103 over Lockerbie, Scotland, in December 1988. Almost exactly one year later, federal Judge Robert Vance was killed when he opened up a package bomb in the seeming safety of his own home. Incredibly, no one was even injured when a 1,000-pound bomb put in place as part of an extortion scheme blew up Harvey's Wagon Wheel Casino in Lake Tahoe, Nev., in 1980. And only six people died when another 1,000-pound bomb almost knocked down the World Trade Center and Vista Hotel in New York City in February 1993.

It's the firm policy of the FBI not to declare that a bombing has taken place until they can prove it. Tom Thurman, who headed the American team investigating the bombing of Pan Am Flight 103 on Dec. 21, 1988, recalled in his soft Kentucky drawl, "When we first heard about it we might have believed it was a bomb, but until we had proof we couldn't say it.

"We spent that first day walking over the hillsides through the mud. At the end of the day we had a meeting. People were reporting in from various sectors what they were doing and what they'd found. As I walked into the operations center someone handed me a piece of broken metal maybe 3 inches wide and 8 or 9 inches long, and asked me if it had any meaning. I knew instantly. It had what we call pitting and cratering. These are marks that look like inverted mushrooms and they're made in metals by superheated gases when an explosion occurs. That's the only time you see them. I took one look at this piece of metal and said, 'OK, now we know we had a bomb.' "

Debris from Pan Am 103 rained over 845 square miles of Scottish countryside. In 1976 a car bomb blew up former Chilean diplomat Orlando Letelier right in the heart of downtown Washington. The World Trade Center was crippled by a bomb that destroyed five levels of the parking garage, knocked out all power to the buildings, and left huge slabs of concrete hanging precariously above tanks filled with potentially explosive Freon.

There is a common misconception that the bomb destroys itself in the blast. Not true. As much as 95 percent of a bomb will survive detonation, although it will be shattered into thousands of pieces. And finding those pieces is often the key to solving the crime.

The investigation can only be as complete as the crime-scene search. Finding out what type of explosive was used, the size of the bomb, where it was placed, and how it was transported are the first steps toward discovering who made it and who planted it. Everything found at a bomb scene can help answer those questions.

"I knew within two hours after entering the World Trade Center what type of bomb we had and how big it was," recalled Dave Williams, of the FBI Criminal Laboratory's Explosive Unit, who was in charge of the investigation at the scene. "I was able to determine where the seat of the explosion was from the way debris had been thrown, the type of damage done to the concrete and steel, the pitting and cratering, the fact that there were flash burns on one side of a pillar but not on the other. You have to look at everything and put it all together.

"The extent of the damage told me, from experience, that the velocity of the explosion was somewhere between 14,000 to 15,000 feet per second. Different explosives detonate at different speeds. Anything faster or slower would have done a different type of damage. C-4 or TNT would have shattered the steel, for example. So, from the velocity, I knew it pretty much had to be a fertilizer-based product.

"We're pretty familiar with the capabilities of fertilizer-based explosives, so from the extent of the damage I was able to estimate that we had about 1,200 pounds of explosives. So how do you get a 1,200-pound bomb into that building? It isn't going to fit comfortably inside a car. The height of the garage door limited the size of a truck. So we guessed it had to have been carried in a 1-ton van or truck. That gave us a direction: It told us we should be looking for the remains of that type of vehicle in the crater."

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