(Court TV) -- Prosecutors in the David Westerfield capital murder trial have hired a top national forensic entomologist in an apparent attempt to neutralize the defense's strongest argument for acquittal -- insect evidence indicating the defendant could not have killed Danielle van Dam.

M. Lee Goff, a professor of forensic sciences at Chaminade University in Hawaii, said that as of Friday morning, he is working for the San Diego District Attorney's office on the case.

"[P]roviding testimony seems to be more important than providing commentary," Goff wrote in an e-mail, explaining why he could no longer comment on the case.

If Goff testifies for the prosecution, he will likely contradict, or at least raise questions about, the testimony of defense expert David Faulkner, who testified last week that insects found in Danielle's decomposed body suggested she had been left outside for a far shorter time than prosecutors claimed.

Danielle, a second-grader who lived two doors from Westerfield, was abducted from her bed the night of February 1. Searchers found her body along a roadside February 27. Faulkner said his analysis showed that flies -- which land almost immediately on dead bodies -- first infested her corpse between February 16 and February 18. Because Westerfield was under police surveillance after February 5, he could not have dumped her body then.

During Faulkner's testimony, prosecutor Jeff Dusek quizzed him about whether unusually warm and dry temperatures in February might have skewed his results, but Faulkner stood by his findings.

Goff trains FBI agents and has testified in cases across the country, including the trial of serial killer Thomas "Zoo Man" Huskey in Tennessee. He is also the author of "A Fly for the Prosecution: How Insect Evidence Helps Solve Crimes," a book that, according to the Washington Post, "anyone who can get past the gross-out factor will find a fascinating read."

Forensic entomologists are a fairly rare breed in the United States. Richard Merritt, a forensic entomologist and professor at Michigan State University, said he only knew of nine North American experts certified by the American Board of Forensic Entomology.

San Diego-based Faulkner does not have a doctorate and is not certified by the board, but both prosecutor Dusek and defense lawyer Steven Feldman have consulted him in previous cases.

Forensic entomology, unlike DNA analysis is "not an exact science," Merritt said, and dueling interpretations of insects found at crime scenes and during autopsy is not uncommon.

"It's not black and white. There's more play because of the environmental factors," he said.

These experts establish the time of a body's first infestation by determining the age of the insects they recover. There are standard life spans for those maggots, flies and sometimes beetles, but temperature can affect how long individual bugs live.

In the "Zoo Man" case, Goff and another forensic entomologist, Neal Haskell, clashed over when insects first entered the corpse of a murdered prostitute. Huskey, a former employee of the Knoxville Zoo, confessed to killing four women in 1992 and pleaded not guilty by reason of insanity.

At his trial, however, his lawyers suggested that one of the women was killed by someone else. Goff said maggots indicated that Huskey was in custody at the time the woman's body was dumped, but Haskell put the time at a few days before his arrest. The jury deadlocked on the mental illness issue, and Huskey will be retried.

Because each scientist has his own method of determining the life spans, the process can lead to disagreement, Merritt said. Rarely, however, does the disagreement concern the 15-day disparity in the Westerfield case.

"A lot of the disagreements involve a variation in one day, two days," said Merritt. "Not over a week and a half. If it's that big a time, someone screwed up."