Forensic Entomology and The Law - Famous Cases - David Westerfield

David Westerfield

In the United States, forensic entomology became well known through the trial of David Westerfield in 2002 for the abduction and murder of seven-year-old Danielle Van Dam. In this San Diego case, the courtroom became a battle over conflicting reports from four forensic entomologists, Dr. David Faulkner, Dr. Neal Haskell, Dr. M. Lee Goff, and Dr. Robert D. Hall. A fifth scientist, Dr. William Rodriguez, a forensic anthropologist, also testified on this issue. Dr. Haskell, Dr. Hall, and Dr. Faulker argued that forensic entomology established that the body of Danielle Van Dam was dumped in mid-February, which proved to be after Westerfield was already under police surveillance (February 5), while Dr. Goff insisted that the victim's body was colonized by larvae earlier than the other three entomologists estimated (his dates were February 9 to 14). His dates were earlier as he used new data from Canada which gives a significantly slower development for that fly species. Dr. Richard Merritt, a forensic entomologist and professor at Michigan State University, stated that because each scientist has his own method, this can lead to disagreement, but a lot of the disagreements involve a variation of one or two days, not over a week and a half as in the Westerfield case: “If it's that big a time, someone screwed up”.

The above dates show that all the entomologists, including the prosecution’s expert (Dr. Goff), gave dates that excluded the defendant by a significant margin - at least four days. Yet the jury rejected that evidence and found him guilty. The foreman explained that he felt “the field was too subjective to exonerate Westerfield”. He said he “considered all but the first of the five scientific experts on the bug issue 'hired guns' ”. So he respected Faulkner’s opinion (because he was brought onto the case by the police), but said that “Faulkner's testimony only gave mid-February as the latest date when Danielle's body could have been exposed to insects, not the earliest”. That is not correct: Faulkner gave the 16th as the earliest date (and the 18th as the latest). If he had given the 16th as the latest date, in other words it could have been much earlier, then the prosecution would have called him as their witness: instead, he was called by the defense.

Goff also did calculations based on the temperatures at the nearby golf course, but didn’t complete them because they gave a date prior to February 2. One reason for this impossibly early date is that the golf course temperatures were lower, but it had an unofficial weather station so its temperatures might not have been accurate (and another nearby golf course, also with an unofficial weather station, recorded much higher temperatures). The other reason is that, although it recorded hourly temperatures, the prosecution had only asked for its daily maximum and minimums, forcing Goff to use an alternative calculation method which systematically underestimates the amount of thermal energy at low temperatures. Nevertheless, this may have helped convince the jury that a date much earlier than the 9th was possible.

The prosecutor, Jeff Dusek, was highly critical of the forensic entomology evidence, in fact he dismissed the field outright. Which is surprising, as he had relied on this science in the past. In particular, in 1992 he used mainly Faulkner’s expert testimony to convict serial rapist Ronald Porter of the murder of Sandra Cwik. Both Dusek and Faulkner appeared in the “Insect Clues” episode of “Forensic Files”, which featured that case. Making his rejection of the entomology evidence in the Westerfield case even more surprising, is that there were similarities between the two cases: both bodies were outdoors in rural areas (the recovery sites were about 20 miles apart), they were uncovered and were exposed to high temperatures, and the maggots were in the third development stage (instar). In the Cwik case, Faulkner’s calculations (and specifically his opinion of the maximum time) had to be accurate to within about 10% for Porter to be guilty; but in the van Dam case, his calculations had to be out by about 100% for Westerfield to be guilty. And making it suspicious is that Dusek claimed, in closing argument in the Westerfield trial, that when Faulkner testified in that trial, they (the prosecution) didn't know anything about bug evidence, didn't know enough to ask him questions, and didn't know anything about entering the third stage.