Defense could pin hopes on insect life
By Kristen Green
STAFF WRITER
June 30, 2002
In the first four weeks of David Westerfield's murder trial, jurors were schooled in scientific evidence such as blood and DNA, fingerprints and fibers. Now they'll get a crash course in the life cycle of flies.
Westerfield's team of lawyers is expected to launch his defense this week, and lead attorney Steven Feldman has hinted that he will use insect biology to prove 7-year-old Danielle van Dam died after police and reporters began tracking his client's every move. That would mean Westerfield couldn't have killed the child.
"This would be very powerful evidence," said San Diego criminal defense lawyer Michael Pancer. "I can't think of what the state would say if this point were pinned."
Using forensic entomology, scientists can estimate when the girl died by determining the age of insects, generally flies, found on her body.
"They generally get to the body before police do, and they lay eggs," said Bernard Greenberg, professor emeritus of biological sciences at the University of Illinois at Chicago.
The prosecution may call the same expert to the witness stand.
Because of the gag order in the case, no one can provide a timetable for witnesses, clarify facts or discuss strategy.
Feldman has raised the possibility that Danielle may have been killed up to two weeks after her mother reported her missing. Her body was dumped in a brushy rural area in East County.
"You're going to be convinced beyond any doubt that it was impossible, impossible for David Westerfield to have dumped Danielle van Dam in that location," he said on the first day of the trial.
Death's timetable
The jury has heard the prosecution's theory of Danielle's death from Dr. Brian Blackbourne, the county medical examiner. He testified that the girl's body could have been in the weeds along Dehesa Road 10 days to six weeks when it was found Feb. 27.
Forensic entomologists believe they can narrow that window of death, and coroners don't disagree.
Forensic entomology, the use of insects in legal cases, has gotten a boost in mainstream recognition from crime television shows such as CBS' "CSI: Crime Scene Investigation," whose main character frequently uses insects to solve crimes. NBC's "Crossing Jordan" also has an insect expert, nicknamed "Bug," in the cast.
In the real world, the application of forensic entomology to crime investigations has become more common since it was introduced in the United States in the 1970s.
Insect biology has been used in a number of San Diego County cases, including that of Daniel Rodrick, who was convicted in 1997 of killing his wife. An entomologist's testimony helped narrow the time that the victim's body probably was dumped in Pala.
The reason attorneys frequently use entomology is that establishing the time of death is difficult for medical examiners, said San Diego insect expert David Faulkner.
"After 24 to 48 hours, things start to get pretty fuzzy," he said.
A medical examiner relies on three factors to make an assessment, Faulkner said: the amount and distribution of rigor mortis, the change in body temperature and the degree of decomposition. But after several days, rigor mortis dissipates and the corpse assumes the temperature of its environment.
Insects can give more specific information because they have a definitive development period that can be meticulously measured, said Faulkner, who collected insects during Danielle's autopsy and is listed as a potential witness by the prosecution and the defense.
He said his testimony will probably be more useful for the defense, but added the gag order prevents him from discussing his findings outside court.
Faulkner described the collecting of insects from a body as painstaking, similar to the collecting of other scientific evidence.
Generally, he said, forensic entomologists go where a body is found and remove insects from the corpse and areas under and near it. They frequently focus on flies, but also look at other insects, including ants and beetles.
Most of the insects are preserved with alcohol so they can be studied later, Faulkner said. Some of the larvae collected are placed in containers with a piece of liver so they can grow to adulthood, which enables scientists to identify each insect with certainty.
The scientists gather climate data, such as daily temperatures and precipitation measurements, for the time the victim was missing.
Weather is important because a fly's development varies according to conditions. Humidity and daytime highs help forensic entomologists better pinpoint the time flies complete a life cycle.
"The insects will tell you when the body was available to them," Faulkner said.
Fly's life and times
Expert witness Jason Byrd, an associate professor at Virginia Commonwealth University in Richmond, Va., said making insects interesting to the jury is difficult.
Flies have a brief life span in warm weather, as short as 21 days. But they can live six months in colder weather.
They are attracted to the corpse's smell, and either lay eggs or deposit larvae. In about a day the eggs hatch into larvae, or maggots, which live on the dead tissue and develop quickly.
Depending on the species and temperature, eggs reach maturity, or the pre-pupal stage, in five to 12 days. From eggs, maggots feed on and then migrate from the body to form the pupal stage, similar to the cocoon stage of the butterfly.
After it leaves the body, a maggot shrinks in size, and the outer covering hardens into what looks like a miniature football. The adult fly develops in that football, called the pupae.
On average, it takes 14 to 24 days for the eggs to reach adult stage, depending on weather.
The longer a body has been left outside, the less precise an entomologist's estimated time of death.
A number of factors can delay insects from reaching a body. For example, burial in a shallow grave, strange weather or wrapping the body in a blanket can delay detection by insects for a few days.
"They'll get there, but they're not going to get there as quickly," said M. Lee Goff, one of eight certified forensic entomologists in the nation and chairman of the forensic sciences department at Chaminade University in Honolulu.
Danielle apparently wasn't wrapped in a blanket or buried in a shallow grave. However, Faulkner has described the weather in February as unusual.
Jurors in the Westerfield trial have heard powerful scientific evidence over the month the prosecution has been presenting its case. But their responsibility is to determine beyond a reasonable doubt whether Westerfield killed the girl, and the defense has not begun.
Witnesses for the prosecution have testified that DNA from a bloodstain on Westerfield's jacket and on the carpet in his motor home matches Danielle's. The victim's DNA was obtained from one of her ribs after the autopsy.
Jurors also have heard that a hair found on a bathmat in Westerfield's motor home could be hers, and DNA tests of a hair found in the motor home's sink drain matched her DNA.
Witnesses also testified that fibers wrapped around the victim's necklace matched fibers found in Westerfield's bedding and laundry, and an expert said two fingerprints found on a cabinet in his motor home were left by her.
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Kristen Green: (619) 542-4576; kristen.green@uniontrib.com
Copyright 2002 Union-Tribune Publishing Co.
