COLUMN ONE : Combing a Crater for Bomb Clues : The nation’s foremost experts began their search of the World Trade Center for evidence only hours after the genie of terrorism was let loose. Their skill got fast results.

In the beginning was a spark, the source of detonation. In a breath, it unleashed the fury of the bomb. For an instant the yellow van contained it, squeezed it within walls of glass and upholstered sheet metal.

Only reluctantly the steel gave way, pulling and stretching and twisting like taffy. Jets of hot gases incinerated paint, seared metal and sprayed patterns of pockmarks across hard metallic surfaces. Finally the forces were irresistible.

In that barely discernible instant, the van disintegrated. It was 12:18 p.m. Friday, Feb. 26. The genie of terrorism was loose in the cavernous underground parking garage of New York’s World Trade Center.

As the van blew apart, the view out Malcomb Brady’s first-floor office window in distant Miami was lush and serene. It overlooks the Doral Country Club. As usual, Brady had parked his car a safe distance from the course, beyond the range of errant drives by Friday duffers. That was a nuisance.

Still, the silver-haired Florida native was going to miss the neighborhood--as well as his old assignment running one of the national bomb response teams for the federal Bureau of Alcohol, Tobacco and Firearms. Headquarters had just promoted him to special agent in charge of the field office in Cleveland.

Brady had not yet begun to pack.

At the same moment in Maryland, ATF agent Dan Boeh was working on his latest bomb investigation at the Baltimore County Police Department. Local authorities had asked for federal assistance after a pipe-bomb attack on the home of a county police officer three months earlier.

They got Boeh, a lanky, slow-talking bomb expert who had been helping unravel crimes of fire and explosion for more than 20 years.

He is also the designated regional team leader of ATF’s national bomb response squad, making him Brady’s chief assistant in event of a major investigation.

The Maryland case was routine. Fragments recovered from the pipe bomb already had led to an arrest. For Boeh, the burden of this Friday afternoon was pretrial paperwork.

But that was before the spark went off in the yellow van on the B2 level in the trade center parking garage, before the devastating chain-reaction brought about six deaths, approximately 1,000 injuries and the greatest investigative test yet for the ATF’s national response team.

Released from the van’s thin shell, the awesome force of the bomb acted with certain predictable traits. It surged for the exits. Just as a fire seeks oxygen, the screaming ball of heat and gas released by a bomb naturally seeks a vent, any avenue of escape, as it slams into walls, ceilings and floors.

With more than 1,000 pounds of raw energy, this explosive device had the power to make its own vents.

A hole 50 feet by 80 feet opened overhead in the steel-reinforced, 21-inch-thick concrete ceiling, wiping out the tower commissary on B1, the level above, and plunging a restaurant employee to his death through the chasm.

Still potent, the blast then pushed upward to the next level of concrete, punching a flower-shaped hole 15 feet by 20 feet in the lobby floor of the posh Vista Hotel.

Simultaneously, the force erupted laterally, spewing bits and pieces of the yellow van in a 360-degree pattern. On one side, a thick wall deflected the force. Unconstrained in other directions, the force fired out like a battery of clenched fists.

A seven-ton steel support beam, secured with welds and rivets, was ripped away and launched like a giant, crude arrow. Fifty feet across the parking chamber, it slammed through a brick wall that collapsed onto the last lunch shared by four maintenance workers in the locker room on the other side.

A nearby four-foot cinder-block wall toppled. Cars lifted off the ground by the blast rolled, tumbled and piled one on top of the next. Other vehicles absorbed the blow: Windows exploded, roofs collapsed in a tell-tale V-shape, gas tanks erupted. Car alarms sounded in a chorus.

Vibration and pressure blew away two-foot-square concrete casements that surrounded structural support columns, the foundation of the hotel. Only bare steel girders remained.

Along one wall, a gray length of metal guard rail was torn from its anchors, spun round and round and reshaped in flight into a jagged basketball-sized object.

Hurled up the parking ramp toward daylight, it shot out the open garage door like a bullet out of a muzzle, smashed through the rear window of a car on West Street and lodged in the dashboard on the vacant passenger side.

Remnants of the van--from tire rims and grill to ash tray and radio dial--were scattering to the furthest regions of the underground garage.

Beneath the van, the 21-inch-thick slab of steel-reinforced concrete floor turned to powder. A 150-square-foot hole swallowed the biggest pieces of the van and anything else in the vicinity. Tons of debris crashed through the floor, piling atop air-conditioning units on B5.

Finally, the force of the blast was spent, leaving behind a choking haze of smoke and dust that began climbing into the office towers.

Searchers groping through the dark chamber soon would discover that the bomb had created an interior canyon 60 feet deep--a hole thereafter called “the crater.”

On the floor of the crater was a three-story heap of mangled pipes, steel, commissary equipment, desks, chunks of concrete, bricks and battered cars. And somewhere in the 2,600-tons of debris was something else: Clues.

*

Brady, 45, left work early that Friday afternoon after hearing the news reports. When someone asked where he was going he said: “Home to pack.” The reports were sketchy, but the description didn’t sound like an accident. Brady was expecting a call from headquarters. His pager beeped just as he got home. It was the call from Washington.

ATF’s national response teams, commonly referred to by the agents as the NRT, are activated only at the request of another agency, such as local police or the FBI. As the nation’s foremost bomb experts, they get a lot of invitations. Most are small jobs.

Brady’s unit, like each of the other three regional teams, includes investigative agents, forensic chemists and explosives technicians who can be plucked from various ATF field offices around the area in times of emergency. His first call was to Baltimore.

Like his supervisor, Boeh, 47, was already packing. Even before Brady could notify the first contingent of 17 agents that night, summoning them to a hastily arranged staff meeting in Lower Manhattan the next day, Boeh already was driving up Interstate 95.

Boeh’s assignment would be to chart a “plan of investigation.” He made his first walk around the twin towers shortly after midnight--12 hours after the explosion. It was too early to go inside. Search and rescue teams were still combing the garage.

In fact, Boeh didn’t get his first view of the bomb scene until after a midday briefing Saturday from FBI agents and the New York Police Department bomb squad.

Boeh had seen a lot of devastation in his years: huge craters in Vietnam from B-52 drops, the aftermath of attacks on abortion clinics, cars blown apart by booby-traps. But he said nothing had prepared him for the crater.

“I was shocked. I wasn’t ready for such damage. Never have I ever seen anything this massive,” he said later.

Late that Saturday afternoon, at the first gathering of his team, Boeh addressed investigators with a soft drawl: “Well, welcome to the mother of all bombings.”

A key element of Boeh’s investigative plan was dictated by conditions. Precariously loose chunks of concrete dangling around the rim of the crater made work in the pit extremely dangerous. The meticulous search for clues would be restricted to the outer fringes until construction workers could shore up the hole. Brady underscored that strategy, declaring: “I will not endanger one guy for one minute for one shred of evidence.”

The first question on Boeh’s mind was where the explosion originated. Already, press accounts were referring to the site as “ground zero.” Finding that precise spot would help determine the best way to search the surrounding area.

Unfortunately, ground zero wasn’t ground at all--it was thin air, the place on B2 where the floor had been.

Boeh went to bed mulling the problem and woke up with a plan. Finding a hardware store open on Sunday, agents obtained 300 feet of rope. At 12-foot intervals--roughly the space between each floor of the parking garage--they tied strips of yellow police tape. Then, from the lobby of the vacant Vista Hotel, Boeh “dropped a plumb line” down through the hole.

The blast damage had a certain symmetry. A line through the center of the smaller hole in the lobby descended through the center of a bigger hole on B1 and on through the center of the biggest hole of all on B2. The yellow tape told the tale, tied to the rope dangling at the vertical center point of the biggest hole.

“That’s where it was,” Boeh declared later. “Right there on the B2 parking ramp.”

Also to be identified was what had carried the bomb, the nature and composition of the explosive, the timing device and detonator.

Boeh’s formal investigative plan had broken down the massive crime scene into a series of small scenes.

With the bomb site roughly determined, he focused primary attention on accessible areas of B2 and the ramps considered most likely to yield the best clues.

Investigators swept down the ramps with brooms and sifters. They swabbed walls with sterile gauze and acetone to recover explosive residue. They rappelled down a section of the crater looking for parts of a vehicle. They picked their way on hands and knees through the devastated B2 locker room, using their fingers and small garden trowels to scoop up debris and pass it through sifters capable of retrieving objects no bigger than an earring post.

But it was an object big enough to trip over that turned the investigation. And it was found that first Sunday in a section of B2 targeted for priority by Boeh’s investigative plan.

ATF bomb technician Joe Hanlin couldn’t be sure at first glance how the deformed piece of metal fit into a vehicle, but years of analyzing the effects of bomb explosions on various materials told him it had been very near the source of the blast. It was, as bomb experts say, “severely stressed.”

Hanlin and a colleague from the New York City police bomb squad noted telltale signs of “feathering,” the effect created when metal under extreme pressure stretches and thins before rupturing.

The investigators also found signs of “bluing,” the result of heat with the intensity of a welding torch scorching blue spots on the gray steel. And they noticed a pattern of pitting, or “dimpling,” caused by the detonation’s gases.

“This looks like something we ought to keep,” Hanlin said.

The part was tagged, photographed and its discovery site noted on a diagram of the crime scene, then sent to the evidence room at the NYPD crime lab, where an inventory of green garbage bags, each filled with other potentially useful debris from the garage, was building up. There, the evidence would be chemically tested and methodically examined for other identification marks.

Boeh was impatient for results of the laboratory analysis. The piece appeared to be part of a vehicle frame, the strongest element of any car or truck.

Nonetheless, it was so badly deformed that the blast must have originated close by. Clearly it was an important piece of the puzzle.

With evidence stacking up in the lab, however, the part still was unexamined the next day. Boeh finally dispatched Hanlin’s Atlanta ATF partner, Terry Byer, to the crime lab to take a closer look at the piece.

A short time later Byer burst into the ATF command trailer with a shout: “All right--we got it!”

Not only was the piece part of the vehicle that carried the bomb, but Byer had been able to find part of a serial number, the nationally registered vehicle identification number.

NYPD and FBI agents began running the numbers through their computers, slowly eliminating vehicles with similar numbers that were nowhere near New York.

Although hampered by finding only a partial serial number, investigators had the advantage of access to computerized vehicle lists provided by manufacturers and state licensing agencies. Now it was only a matter of time before the bomb-carrying vehicle would be identified.

Byer and Boeh exchanged “high fives.” Then they went back to searching for more clues.

By Wednesday, barely five days after the blast, investigators linked Hanlin’s piece of debris to a yellow rental van owned by the Ryder Truck Co. That afternoon FBI agents called on the Jersey City office that had rented the van to Mohammed A. Salameh. A day later, the Palestinian immigrant was in custody, the first suspect charged with aiding and abetting the bombing.

An Egyptian official in New York, marveling at the speed of the breakthrough, said later that he thought terrorists around the world would be startled by the outcome.

“They are not accustomed to such skill and sophistication by police investigators,” observed Abdulaleem Abyad, minister of information at Egypt’s mission to the United Nations.

The investigation continues.

Members of the national response team are still in the crater sifting through debris in search of timing and detonation devices, parts that can be smaller than a pencil’s eraser but of enormous value linking suspects to the crime.

“What a lot of people don’t understand is that an explosion doesn’t destroy the evidence--it just makes it smaller,” Brady said. “And eventually, if we sift long enough, we’ll find what we’re looking for.”