Patricia Cornwell - Point of Origin

'Another metal shaving,' I explained to her. 'I hate to spring this on you, Mary, but if you could look at it now. It's urgent.'

'Another case or the same one?'

'The fire in Lehigh County, Pennsylvania,' I replied.

'No kidding?' She looked surprised as she slit taped brown paper with a scalpel. 'Lord,' she said, 'that one sounds pretty awful, based on what I heard on the news, anyway. Then the FBI guy, too. Weird, weird, weird.'

She had no reason to know about my relationship with Benton.

'Between those cases and the one in Warrenton, you have to wonder if there isn't some whacko pyro on the loose,' she went on.

'That's what we're trying to find out,' I said.

Chan took the cap off the small metal evidence button and with tweezers removed a layer of snowy cotton, revealing the two tiny bright turnings. She pushed back her roller chair to a counter behind her and proceeded to place a double-sided adhesive square of black carbon tape on a tiny aluminum stub. On this she mounted the shaving that seemed to have the most surface area. It was maybe half the size of a normal eyelash. She turned on a stereo-optical microscope, positioned the sample on the stage, and adjusted the light wand to take a look at a lower magnification before she resorted to the SEM.

'I'm seeing two different surfaces,' she said as she adjusted the focus. 'One real shiny, the other sort of dull gray.'

'That's different from the Warrenton sample,' I said. 'Both surfaces were shiny, right?'

'Correct. My guess would be that one of the surfaces here was exposed to atmospheric oxidation. For whatever reason that might be.'

'Do you mind?' I asked.

She scooted out of the way and I peered through the lenses. At a magnification of four, the metal turning looked like a ribbon of crumpled foil, and I could just barely make out the fine striations left by whatever had been used to shave the metal. Mary took several Polaroid photographs and then rolled her chair back to the SEM console. She pushed a button to vent the chamber, or release the vacuum.

'This will take a few minutes,' she said to us. 'You can wait or go and come back.'

'I'm getting coffee,' said Marino, who had never been a fan of sophisticated technology and most likely wanted to smoke.

Chan opened a valve to fill the chamber with nitrogen to keep contamination, such as moisture, out. Next she pushed a button on the console and placed our sample on an electron optics table.

'Now we got to get it to ten to the minus six millimeters of mercury. That's the vacuum level needed to turn on the beam. Usually takes two or three minutes. But I like to pump it down a little more than that to get a really good vacuum,' she explained, reaching for her coffee. 'I think the news accounts are very confusing,' she then said. 'A lot of innuendo.'

'So what else is new?' I commented wryly.

'Tell me about it. Whenever I read accounts of my court testimony, I always wonder if someone else had been on the stand instead of me. My point is, first they drag Sparkes into it, and to be honest, I was about to think that maybe he had burned his own place and some girl. Probably for money, and to get rid of her because she knew something. Then, lo and behold, there are these two other fires in Pennsylvania, and two more people killed, and there's the suggestion all of it's related? And where's Sparkes been during all this?'

She reached for her coffee.

'Excuse me, Dr Scarpetta. I didn't even ask. Can I get you some?'

'No thank you,' I said.

I watched the green light move across the gauge as the mercury level slowly climbed.

'I also find it odd that this psycho woman escapes from the loony bin in New York - what's her name? Carrie something? And the FBI profiler guy in charge of that investigation suddenly ends up dead. I think we're ready to go,' she said.

She turned on the electron beam and the video display. The magnification was set for five hundred, and she turned it down and we began to get a picture of the filament's current on the screen. At first it looked like a wave, then it began to flatten. She hit more keys, backing off the magnification again, this time to twenty, and we began to get a picture of the signals coming off the sample.

'I'll change the spot size of the beam to get a little more energy.'

She adjusted buttons and dials as she worked.

'Looks like our shaving of metal, almost like a curled ribbon,' she announced.

The topography was simply an enlarged version of what we had seen under the optical microscope moments earlier, and since the picture wasn't terribly bright, this suggested an element with a lower atomic number. She adjusted the scanning speed of the live picture and took away some of the noise, which looked like a snowstorm on the screen.

'Here you can clearly see the shiny versus the gray,' she said.

'And you think that's due to oxidation,' I said, pulling up a chair.

'Well, you've got two surfaces of the same material. I would venture that the shiny side was recently shaved while the other wasn't.'

'Makes sense to me.'

The crinkled metal looked like shrapnel suspended in space.

'We had a case last year,' Chan spoke again as she pressed the frame store button to make photographs for me. 'A guy bludgeoned with a pipe from a machine shop. And tissue from his scalp had a metal filing from a lathe. It was transferred right into the wound. Okay, let's change the back scatter image and see what kind of X-ray we get off that.'

The video screen went gray and digital seconds began to count. Mary worked other buttons on her control panel, and a bright orange spectrum suddenly appeared on the screen against a background of vivid blue. She moved the cursor and expanded what looked like a psychedelic stalagmite.

'Let's see if there are other metals.'

She made more adjustments.

'Nope,' she said. 'It's very clean. Think we got our same suspect again. We'll call up magnesium and see if there's an overlapping of lines.'

She superimposed the spectrum for magnesium over the one for our sample, and they were the same. She called up a table of elements on the video screen, and the square for magnesium was lit up red. We had confirmed our element, and although I had expected the answer we got, I was still stunned by it.

'Do you have any explanation as to why pure magnesium might be transferred to a wound?' I asked Chan as Marino returned.

'Well, I told you my pipe story,' she replied.

'What pipe?' Marino said.

'Only thing I can think of is a metal shop,' Chan went on. 'But I would think that machining magnesium would be unusual. I mean, I can't imagine what for.'

'Thanks, Mary. We've got one more stop to go, but I'm going to need you to let me have the shaving from the Warrenton case so I can take it over to firearms.'

She glanced at her watch as the phone rang again, and I could only imagine the caseload awaiting her.

'Right away,' she said to me generously.

The firearms and toolmarks labs were on the same floor and were really the same section of science, since the lands and grooves and firing pin impressions left on cartridge cases and bullets were, in fact, the toolmarks made by guns. The space in the new building was a stadium compared to the old, and this spoke sadly to the continuing deterioration of the society beyond our doors.

It was not unusual for schoolchildren to hide handguns in their lockers, or show them off in the bathrooms, and carry them on the school bus, it seemed, and it was nothing for violent offenders to be eleven and twelve years old. Guns were still the top choice for killing oneself or one's spouse, or even the neighbor with the constantly barking dog. More frightening were the disgruntled and insane who entered public places and started blasting away, explaining why my office and the lobby were protected by bulletproof glass.