A government scientist on the fourth floor of a glass-faced building here peers through a microscope so powerful that a tiny groove on a nail appears a big as hand.
The gouge on the metal shard - a piece of a nail found near the Jan. 29 abortion clinic bombing in Birmingham, Ala., - looks familiar. A quick check uncovers a strikingly similar marking on the 1-1/2-inch flooring nails used as shrapnel in two bombs set off at a Sandy Springs, Ga., abortion clinic last year.
In fact, the grooves are so nearly identical they appear to have come from the same production batch.
That discovery, in the early days of the investigation, was one of the first pieces of evidence linking the Birmingham bombing to three blasts in Atlanta. By mid-February, federal agents had found another link: Nails found in a storage shed rented by Eric Robert Rudolph bore the same marks.
In the weeks since the Birmingham blast, Mr. Rudolph has become the prime suspect. Federal agents are now hunting for him in the mountains of western North Carolina.
The nails are just one of many intriguing clues linking Rudolph to the bombings that have come out of the labs of the Bureau of Alcohol, Tobacco and Firearms. The Federal Bureau of Investigation and ATF so far officially deny any links. But Tuesday, a single federal task force was formed to coordinate the investigation of the four bombings in Georgia and Alabama.
ATF research shows that steel plates and traces of nitroglycerine may also tie Rudolph to one or more of the bombings. And these discoveries offer a window on how forensic scientists use the latest technology to turn the detritus left by a bomb into tantalizing leads for federal gumshoes.
"Fifteen years ago, we were still using test-tube technology for the majority of our work. Now it's almost all done with high-tech instruments," says Marvin Rennert, chief of the ATF forensics science lab in Atlanta. "There's always new technology and it's always getting more precise."
Send in the dogs
Within hours of the blast, ATF scientists arrived at the Birmingham abortion clinic, ducking under the yellow tape outlining the bomb site.
Led by Labrador retrievers trained to sniff the rubble for traces of explosives, ATF agents painstakingly picked up shards of metal and plastic and place them into shiny, stainless-steel paint cans.
Preliminary testing is done on site with a makeshift mobile laboratory - an innovation first used in the investigations of TWA Flight 800. Speed is critical. The earlier agents can focus an investigation, the hotter the trail.
"The more specific we can be with our identifying materials, the more investigators have to go on," Mr. Rennert says.
After the Birmingham explosion, scientists quickly "read" the bomb debris enough to know that it was ignited by dynamite, not a less-explosive powder, and that nails were included in the bomb.
This information is passed on to investigators, who use it to begin interviewing local hardware store employees, asking them if they have sold a large number of flooring nails to anyone recently and to contact places where dynamite is sold, interviewing those proprietors as well.
ATF scientists are able to draw that conclusion rather quickly because dynamite is a highly destructive explosive. It leaves behind debris that is smaller, sharper-edged than other explosive materials, say experts. And it tends to leave less evidence.
To confirm that deduction, debris was taken to a mobile lab parked on a side street near the clinic. It was mixed with a solvent and placed in a gas chromatograph, a machine the size of a small refrigerator.
The whole brew is heated until it vaporizes. The chromatograph reads the gas and spits out a printout of the particles' ingredients that looks like a series of peaks and valleys. Each squiggle tells scientists how much oxygen, carbon, or other chemical exists in the gas.
In this case, the graph of ingredients probably provided a fingerprint of nitroglycerin, an explosive component of dynamite. A cardboard-bound book of printouts enables scientists to compare the peaks and valleys and confirm the match.
These early conclusions are only the start of the process. At each bombing site, scientists and investigators gather several trash bags' worth of debris. Once they have collected every bit of metal and plastic, scraped and swabbed all useful particles, they take all of this evidence back to their regional lab in Atlanta - one of three ATF forensic labs in the country.
It is here that links were found between pieces of 1/8-inch-thick steel plates among the debris of the 1996 summer Olympics bombing and two bombs at an Atlanta abortion clinic. At the site of the Otherside Lounge bombing in Atlanta, 1/4-inch-thick plates, of the same material, were found. Investigators suspect that the plates were used to direct the blast.
FBI agents have not confirmed reports that they have found a metal shop in western North Carolina where steel plates used in all three Atlanta bombings came from. But a former employee of the Franklin Machine Co. in Franklin, N.C., has told reporters that the FBI questioned him and told him that they had evidence linking the bombings to the shop. A friend of Rudolph's worked at the machine shop.
If the reports are true, ATF scientists likely led the FBI to this conclusion through the following process:
After each bombing, scientists recovered and catalogued pieces of the various steel plates. At the lab, they would have used an electron microscope to analyze the makeup of the metal chips.
They would have placed the metal in the chamber of the microscope and turned on the attached X-ray machine. This attachment bombards the metal with rays. A computer deciphers the way the rays bounce back and prints out an analysis of what elements the steel contains: some combination of iron, carbon, and possibly nickel or magnesium.
A match made of metal?
Their scientific sleuthing likely uncovered a peculiar mix of metal that matched a batch that was recovered from the machine shop in Franklin.
"It's my understanding that the metal plate is far more important than any other of the bomb components," says Neil Livingstone, a Washington-based terrorism consultant who has followed the bombing cases closely. "There appears to be some uniqueness to the metal plates that suggests they were all made in same place. There's a particular composition that's not something you'd find just anywhere."
The scientists work also includes analysis away from the bomb site. In the Birmingham case, ATF scientists were deployed to North Carolina once suspect Rudolph's truck, locker, and mobile home were identified. It was here that traces of nitroglycerin were reportedly found in Rudolph's truck.
The initial lead in the case came from a witness who saw a man leaving the bombing scene in a truck. The license plate tied Rudolph to the truck. This was enough to name Rudolph as a material witness. But it took the scientific evidence - nitroglycerin swabbed with a cotton square off the radio dials, steering wheel, and seat and processed back at the lab - to name Rudolph as a suspect.
As this case has shown to date, scientists work hand-in-hand with investigators, each relying on the other to provide evidence for the case. While ATF officials are loath to discuss the details of this ongoing investigation, the process of scientific deduction seldom varies.
"We move from a rather coarse look, identifying things you could see and begin to recognize first," says Rennert. "So you say, 'That may be part of pipe.' Then you go on and say, 'That appears to be a PCB pipe.' And then, 'Not only, is it a PCB pipe, it's this particular brand of PCB pipe.' And that's how we work. Each step is more and more specific."