On July 21, 1988, Sandra Cwik’s body was discovered in the mountains near San Diego, California. She had been murdered. Ronald Porter was arrested for the crime.
(The case was on the “Insect Clues” episode of “Forensic Files” https://www.youtube.com/watch?v=33INHGh16IE.)
At his trial, the strongest evidence against him was the entomology. Based on testimony by Law Enforcement’s regular forensic entomologist, she had died on the night of July 17. (Quoting the narrator, “Sandra Cwik was still alive when the Sun set on Sunday evening July 17th but she was dead by daybreak on Monday morning July 18th ”. Porter didn’t have an alibi for that time, so he was convicted and sentenced to life.
So Forensic Entomology is very accurate and trustworthy. Right? Wrong!
Just ten years later, Danielle van Dam went missing from her home in San Diego. The police almost immediately suspected her neighbor, David Westerfield, because he had gone to the distant desert that weekend (even though that’s something he often did). So he was promptly placed under round-the-clock surveillance. Three weeks later, her body was discovered. (It wasn’t anywhere near that desert, in fact it was relatively close to her home and just a few miles from where Cwik’s body had been found.)
Once again, Law Enforcement called in their regular expert. After doing his calculations, he gave his dates which implied that she had only died about two weeks after Westerfield was being surveilled. So he couldn’t possibly have done it: right? But he had already been arrested, and they didn’t release him, instead, they proceeded to trial.
At his trial, their regular entomology expert testified instead for the defense (!), who also brought in two other entomology experts (one of whom is internationally known) who supported his conclusion. The prosecution brought in their own expert, and he ALSO gave dates that excluded Westerfield - but added that it could have been earlier.
As luck would have it, Westerfield had the same prosecutor as Porter. In Porter’s trial, the prosecutor argued for the accuracy of entomology; but in Westerfield’s trial, in stark contrast, he trashed the science.
The jury rejected the entomology evidence - and the fact that there was no evidence of Westerfield at either of the crime scenes (the kidnapping and the recovery sites), and found him guilty anyway. He was sentenced to death and has been on death row ever since.
That case, like the Petito-Laundrie case, was high profile, and the police had persuaded the media and the community of the suspect’s guilt. So even if entomology evidence strongly points to Laundrie’s innocence, there’s a good chance he will be arrested, tried and convicted anyway.
Larvae development, on which the entomology evidence is based, depends heavily on temperature. In Gabby’s case, I don’t know what the weather in that Grand Teton Park was like over the past month, but at Jackson Hole Airport, which is presumably nearby, maximum temperatures have mostly been above 70F, even sometimes above 80F, so larvae development would have been fairly rapid, and so would have been body decomposition, which could complicate autopsy findings.