“I've also found that all fatty acid values are highest just after maggot migration.”
“When larvae abandon the corpse to pupate.”
“Yes. Until that point the presence of the insects tends to restrict the flow of body fluids into the soil.”
“Doesn't pupation occur at approximately four hundred ADD?” ADD stands for “accumulated degree days,” a figure calculated by summing average daily temperatures.
“With some variation. Which brings up a good point. VFA production is temperature dependent. That's why it can be used to determine time since death.”
“Because a corpse will produce the same ratios of propionic, butyric, and valeric acids for any given accumulated degree days.”
“Exactly. So the volatile fatty acid profile can provide an estimate of TSD.” TSD is the investigator's shorthand for “time since death.”
“Did you get the National Weather Service data?”
He went to a set of shelves and returned with a printout.
“It was amazingly fast. Normally it takes much longer. But we do have a slight problem. For a really accurate TSD estimate I need three things. First, the specific fatty acid ratios.”
He pointed at a computer screen linked to the gas chromatograph.
“We'll have those shortly. Second, the National Weather Service data at the location where the corpse was found.”
He held up the printout.
“Third, information on the weight and condition of the corpse. And you ain't got no body.” He sang the last.
“Everyone's a comedian.”
“Two variables are important: the amount of moisture in the soil, and the weight of the body prior to decomposition. Because everyone has a different ratio of fat and muscle tissue, if I don't have a body, I use a standard of one hundred fifty pounds, then apply a correction factor. I think we're safe in assuming your deceased weighed between one hundred and three hundred pounds?”
“Yes. But in doing this, our range broadens, right?”
“Unfortunately. Did you try a rule-of-thumb estimate?”
Since volatile fatty acid liberation ceases at accumulated degree days 1,285 plus or minus 110, it is possible to obtain a rough estimate of time since death by dividing the average daily temperature on the day a corpse is found into 1,285. I'd done this for Lucy Crowe. Yesterday's average temperature in Bryson City was 18°C (64°F), yielding a maximum time since death of seventy-one days.
“That would be the date on which full skeletonization had taken place, and no more VFAs would be detectable.”
Laslo looked at the wall clock.
“Let's see how accurate you were.”
He rose, filtered and vortexed the soil solution sample, tested its acidity, then placed the tube into the gas chromatograph. After closing and sealing the chamber, and adjusting the settings, he turned back to me.
“Let's give this a few minutes. Coffee?”
When we returned the screen showed a series of peaks in varying colors, and a list of components and their concentrations.
“Each curve shows the concentration of a volatile fatty acid per gram of dry weight of soil. First I'll correct for dilution and soil moisture.”
He hit a few keys.
“Now I can calculate an ADD for each VFA.”
He started with butyric acid.
“Seven hundred accumulated degree days.”
He performed more calculations, using each acid. With one exception the ADDs fell within the 675 to 775 range.
“Now I'll use the National Weather Service data to determine the number of days needed to obtain 675 to 775 accumulated degree days. We may have to adjust later if the readings at your body site differ from the officially recorded temperatures. Normally, I like to know that in advance, but it's not a major problem.”
A few more keystrokes. I held my breath.
“Forty-one to forty-eight days. That's your range. According to your calculation, full skeletonization would have taken place in seventy-one days.”
“So death occurred six to seven weeks ago.”
He nodded. “But keep in mind that this time frame is based on an estimated, not an actual, predeath weight.”
“And at the time the stain was produced, the body was fleshed and actively decomposing.”
He nodded.
“But I ain't got no body.”
