Bugs: The best witnesses?
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On one side there are Danielle van Dam's fingerprints, her blood drops, strands of the 7-year-old's blond locks, hair from a dog like her weimaraner and carpet fibers that seem to be from her room. There is child pornography and a convoluted alibi even the defendant calls "weird."
On the other side, the side for David Westerfield's acquittal, there are bugs.
The pile of evidence painstakingly assembled by prosecutors in Westerfield's capital murder case got a jolt last week from an entomologist who suggested that insect evidence from the 7-year-old's body may exonerate the defendant, who is accused of abducting Danielle from her bedroom, killing her and then dumping her body.
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| Westerfield |
Its practitioners say forensic entomology, which stretches back to 13th century China and has gradually gained acceptance in American courtrooms over the past two decades, is both art and science. There are only nine certified forensic entomologists in North America and about 30 more who offer their expertise in criminal cases without certification.
When done correctly, a study of flies, maggots and beetles at a crime scene can yield crucial evidence about a victim's death, including the time and location, whether the victim had drugs in his system, and in some cases even the DNA of the perpetrator.
But more than other forensic sciences like DNA analysis, forensic entomology eschews straightforward analysis. For analysis concerning time of death — by far the most common task for entomologists in criminal cases — there are no mathematical formulas, no easy calculations. Accuracy depends on the scientist's ability to determine how a host of variables at the crime scene, including temperature, precipitation, time of day, humidity and geography, affected insect life.
"If you are not a very imaginative person as a scientist, you won't go far," said K.C. Kim, a Penn State professor and certified forensic entomologist.
The subjectivity of the field makes for what another forensic entomologist, Jason Byrd of Virginia Commonwealth University, calls "showdowns" — professional disputes over results. According to Byrd, haggling over conclusions has become increasingly common in the last three or four years as lawyers have become more familiar with the evidence and how to attack its credibility.
"A court case with a single entomologist is a thing of the past," said Byrd, a certified entomologist who consults on about 100 criminal cases a year.
A "showdown" seems likely in the Westerfield case. Just two days after damaging testimony from the defense entomologist, the San Diego district attorney's office hired M. Lee Goff, an entomologist from Chaminade University in Hawaii, to consult on the case.
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| Faulkner |
The defense expert, David Faulkner, is particularly difficult to attack because he was initially hired by the prosecution. Faulkner, a research associate at the San Diego Natural History Museum, attended Danielle's autopsy and collected insects from her remains.
Searchers found the second-grader in a trash-strewn lot three and a half weeks after she vanished. Her body was badly decomposed and the medical examiner could only offer prosecutors a wide range — 10 days to six weeks — for her time of death.
Investigators hoped Faulkner could narrow that window to Feb. 2, 3 or 4, the days immediately following Danielle's abduction when Westerfield's activities seemed suspect. Faulkner examined maggots from her body and told authorities the insects began growing 10 to 12 days prior, putting the first infestation between Feb. 16 and Feb. 18. Infestation can start as soon as 20 minutes after a dead body is dumped outdoors.
Faulkner's conclusion did not fit prosecutors' theory. Westerfield was under constant police surveillance from Feb. 5 until his arrest, offering him no opportunity to dump her body in the window of time the entomologist's testimony indicated. Faulkner quickly became a witness for the defense.
The lives of insects
If prosecutors get Goff or another expert to rebut Faulkner's findings, he or she will likely attack the defense expert on how he calculated the post-mortem interval (PMI), entomologist-speak for the first infestation.
Insect life arrives at a dead body in stages. Immediately, flies land on a body. In as little as 20 minutes, they lay eggs. Those eggs hatch into maggots in a day, and those maggots feed on the body. The maggots molt repeatedly, and each stage of larvae is slightly larger, indicating to entomologists how long the insects have lived in the body. Beetles also are attracted to decaying flesh, and the size of their larvae also indicate the time they have been at the body.
But just recognizing the size of the larvae is not enough. Entomologists must also determine the growth rate of the insects. There are two ways to do this. Experts can simply match the size to textbook tables showing the rapidity of growth in a climate-controlled laboratory or they can try to determine the growth rate by themselves. The latter is considered the most accurate, but also the most difficult.
"It has a lot to do with the investigator's experience and intelligence and that has a lot more to do with art than science," said Kim of calculating the PMI.
Among the crucial factors is weather. Hot temperatures mean quick growth, cold temperatures mean slow or no growth. Wind affects the rate as does access to water and other forms of food, like trash cans. Rain and humidity play a role, as well as exposure to sunlight.
In the Westerfield case, prosecutor Jeff Dusek grilled Faulkner about how February's hot, dry weather might have affected his PMI conclusion. Faulkner acknowledged there were fewer flies last winter in San Diego than ever before, but refused to budge off his estimate.
Entomologists also consider unnatural factors, like whether a blanket or sheet around the victim may have retarded insect life. Goff once worked on a case in Hawaii involving a woman missing 13 days. She was discovered murdered and wrapped in blankets. The life stages of the insects indicated a PMI 10 and a half days prior. To determine how the blankets affected the PMI, Goff wrapped a pig carcass in blankets and left it in his backyard. He found it took two and a half days for the flies to penetrate the blanket.
Dusek quizzed Faulkner about the impact of some sort of shroud in the Westerfield case. There is no evidence Danielle's body was wrapped in a blanket, but the prosecutor got Faulkner to admit that a covering, perhaps later dragged away by animals, might have skewed his results.
Will the jury care?
But even when there are disagreements between entomologists on results, they rarely involve as wide a gap as in the Westerfield case.
"A lot of the disagreements involve a variation in one day, two days," said Richard Merritt, a certified forensic entomologist and professor at Michigan State University. "Not over a week and a half. If it's that big a time, someone screwed up."
If the prosecution cannot find an expert who substantially disagrees with Faulkner, the bug evidence would appear to be the defense's chief argument to jurors at closings.
The defense has tried to chip away at the other forensic evidence. Defense lawyer Steven Feldman has suggested Danielle secretly played in Westerfield's motor home and left hair, blood and fingerprints on that occasion. Evidence in his home, the lawyer has hinted, might have been deposited when the girl and her mother sold him Girl Scout cookies. And fiber evidence could have been transferred when Danielle's mother was dancing with Westerfield the night of the abduction.
None of those explanations carry the certainty of Faulker's testimony. But just how persuasive Faulkner's testimony will ultimately be is a subject of hot debate in San Diego, where the case dominates the media.
Former prosecutor Colin Murray said the mountain of other physical evidence pointing toward Westerfield's guilt made the insect evidence little more than a footnote.
"You're asking a lot of this jury to acquit this guy on capital charges based on the presence of bugs," he said. Even without a rebutting witness, Murray said, prosecutor Dusek could undermine the entomological evidence in closings by harping on the subjectivity of the field and asking the panel to instead rely on common sense.
"Common sense tells you, if you're just looking at her body, that it's been out there a long time. It's severely decomposed," said Murray.
But Curt Owen, a retired public defender, disagreed, saying that depending on how the prosecution rebuts the evidence, the case could end in a hung jury or even acquittal.
"It may not be enough to say he's innocent," Owen said, "but it certainly is enough to introduce reasonable doubt."