Postmortem(94)

The fact was we had no break in the case. I’d indefinitely banished Margaret from her office and the computer was to be left in answer mode. Wesley had set up a tracer to track all calls made to her extension. We were going to use the computer to lure the murderer by having Abby’s paper print a story claiming the forensic investigation had come up with a “significant link.”

“He’s going to be paranoid, upset enough to believe it,” I predicted. “If he’s ever been treated in a hospital around here, for example, he’s going to worry now that we might track him through old charts. If he gets any special medications from a pharmacy, he’s got that to worry about, too.”

All of this hinged on the peculiar odor Matt Petersen mentioned to the police. There was no other “evidence” to which we could safely allude.

The one piece of evidence the killer would have trouble with was DNA.

I could bluff him from hell to breakfast with it, and it might not even be a bluff.

Several days ago, I had gotten copies of the reports from the first two cases. I studied the vertical array of bands of varying shades and widths, patterns that looked remarkably like the bar codes stamped on supermarket packaged foods. There were three radioactive probes in each case, and the position of the bands in each probe for Patty Lewis’s case was indistinguishable from the position of the bands in the three probes in Brenda Steppe’s.

“Of course this doesn’t give us his identity,” I explained to Abby and Wesley. “All we can say is if he’s black, then only one out of 135 million men theoretically can fit the same pattern. If he’s Caucasian, only one out of 500 million men.”

DNA is the microcosm of the total person, his life code. Genetic engineers in a private laboratory in New York had isolated the DNA from the samples of seminal fluid I collected. They snipped the samples at specific sites, and the fragments migrated to discrete regions of an electrically charged surface covered with a thick gel. A positively charged pole was at one end of the surface, a negatively charged pole at the other.

“DNA carries a negative charge,” I went on. “Opposites attract.”

The shorter fragments traveled farther and faster in the positive direction than the longer ones did, and the fragments spread out across the gel, forming the band pattern. This was transferred to a nylon membrane and exposed to a probe.

“I don’t get it,” Abby interrupted. “What probe?”

I explained. “The killer’s double-stranded DNA fragments were broken, or denatured, into single strands. In more simplistic terms, they were unzipped like a zipper. The probe is a solution of single-stranded DNA of a specific base sequence that’s labeled with a radioactive marker. When the solution, or probe, was washed over the nylon membrane, the probe sought out and bonded with complementary single strands—with the killer’s complementary single strands.”

“So the zipper is zipped back up?” she asked. “But it’s radioactive now?”

“The point is that his pattern can now be visualized on X-ray film,” I said.

“Yeah, his bar code. Too bad we can’t run it over a scanner and come up with his name,” Wesley dryly added.

“Everything about him is there,” I continued. “The problem is the technology isn’t sophisticated enough yet to read the specifics, such as genetic defects, eye and hair color, that sort of thing. There are so many bands present covering so many points in the person’s genetic makeup it’s simply too complex to definitively make anything more out of it than a match or a nonmatch.”

“But the killer doesn’t know that.” Wesley looked speculatively at me.

“That’s right.”

“Not unless he’s a scientist or something,” Abby interjected.

“We’ll assume he isn’t,” I told them. “I suspect he never gave DNA profiling a thought until he started reading about it in the papers. I doubt he understands the concept very well.”

“I’ll explain the procedure in my story,” Abby thought out loud. “I’ll make him understand it just enough to freak him.”

“Just enough to make him think we know about his defect,” Wesley agreed. “If he has a defect . . . That’s what worries me, Kay.” He looked levelly at me. “What if he doesn’t?”

I patiently went over it again. “What continues to stand out to me is Matt Petersen’s reference to ’pan-cakes,’ to the smell inside the bedroom reminding him of pancakes, of something sweet but sweaty.”

“Maple syrup,” Wesley recalled.