Part 32 (1/2)
”Perhaps I should explain our statistical treatment. We do cl.u.s.ter a.n.a.lysis, to determine the cl.u.s.ters I just described.” Suskind made a honking sound, which I a.s.sumed to be laughter. ”Of course. That's why it's called cl.u.s.ter a.n.a.lysis.”
I sketched a bill.
”To compare the control samples to the victim samples, we use a transfer function called modern a.n.a.log technique. We calculate the dissimilarity between a victim sample and the most similar control sample, using the squared chord distance as the dissimilarity coefficient-”
”May we also leave quant.i.tative a.n.a.lysis for the report?”
”Of course. The bottom line. We found that the diatom a.s.semblages recovered from the sock show strong similarity to samples taken from the midlake channel and from the lakesh.o.r.e.”
Webbed feet.
”Our a.n.a.log matching technique suggests that the closest lakesh.o.r.e a.n.a.logy is with a control sample collected at the bottom of a boat ramp situated in the Bois-de-L'ile-Bizard nature preserve, not far from the body recovery site.”
My pen froze.
”You can pinpoint with that much precision?”
”Of course. What we do-”
”Where is this park?”
She told me. I wrote it down.
”What about the bone plug?”
”I'm afraid that's a bit more complex.”
Suskind now had my full attention. ”Go on.”
”The diatom flora from the bone's outer surface is similar to that recovered from the sock. We recovered no diatoms from the marrow cavity.”
”Meaning?”
”Interpretation of negative evidence is always risky.”
”Suggest some scenarios.”
”Diatoms find their way into the body via inhalation, via ingestion, and via the aspiration of water. Whatever the initial pathway, a.s.suming they are sufficiently tiny, the diatoms then circulate into the body's organs and marrow. Diatoms are recovered from the bone marrow of approximately thirty percent of all drowning victims. They occur at significantly lower rates, perhaps as low as ten percent, in cases of bathtub or other city water drownings.”
”Because diatoms and other impurities are filtered out of domestic water,” I guessed.
”Of course. If present in domestic water, they've most likely come from household cleaners. But those are unique and recognizable species.”
”You found none.”
”We found nothing in the marrow cavity.”
”So it's possible the victim may have drowned in treated or filtered water, not in the river?”
”It's possible. But let me continue. The diatom concentration in bone marrow is usually proportionate to the diatom concentration in the drowning medium. That concentration varies due to the natural cycle of blooms and die-offs. In the northern hemisphere, diatom blooms occur in the spring and fall, creating persistently high levels in rivers and lakes throughout the summer. In winter, levels are typically at their lowest.”
”So the victim could have drowned in the river, but before this season's bloom.”
”It's another possibility.”
”When did this season's bloom occur?”
”April.”
I was scribbling notes next to my doodles.
”Aspiration of water is required to transport the diatoms,” Suskind continued. ”The transportation process works because diatoms are resistant to the mucus of the respiratory system and are able to embolize from the circulatory system into the internal organs.”
I knew where she was going. ”Blood has to be pumping to get diatoms into the marrow.”
”Of course.”
”So the victim may not have been breathing when she hit the water.”
”It's another possibility. But remember. Diatoms are found in only one third of all drowning cases.”
”Why such a low percentage?”
”Many reasons. I'll give you the primary three. First, it may have to do with method of collection. If very few diatoms are present in the marrow cavity, they may simply be missed in sampling. Second, victims who hyperventilate and pa.s.s out under water or who experience laryngeal spasm may die more quickly, leading to a reduced quant.i.ty of inhaled water. Third, as I am sure you know, a relatively low volume of blood flows to and through the bone and bone marrow. And, for this individual, one bone plug was all I had. No samples from lungs, brain, kidney, liver, spleen.”
”When may I expect your report?”
”I'm completing it now.”
Thanking Suskind, I disconnected.
Great. The girl drowned or didn't. In the river or elsewhere.
But the boat ramp. That was useful.
I called, but Ryan didn't answer his cell. Of course. He was in court. I left a message.
The receiver had barely hit the cradle when the phone rang again.
”Having a nice day, kitten?” Male. Unaccented English.
”Who is this?”
”No matter.”
My mind looked for matches.