Crime Library: Criminal Minds and Methods

Donald Blom: A Repeat Sex Offender Finally Stopped

The Tooth in the Fire Pit

Investigators searched Blom's residence and took various items, although no official statements were made at the time about what the items were or how they figured into the investigation. Another search was conducted on Blom's 20-acre Moose Lake property, and over one hundred members of the National Guard and several hundred volunteers participated. They went several miles beyond his property, into the woods, but by evening they had to call it quits. The next morning, the search was resumed with renewed vigor, and Katie's mother said that she had a gut feeling that they would find her daughter alive. Apparently, some hoped the girl was being held somewhere against her will, but the sheriff was less optimistic.

Ashes from Donald Blom's Firepit
Ashes from Donald Blom's Firepit

That morning of the second day, among ashes inside a fire pit on Blom's property, searchers found fragments that appeared to be bone. These went to a lab for further testing. They were positively identified as bone fragments and possibly a tooth, which was sent to odontologists, experts in dental remains.

Board-certified forensic dental expert Dr Ann Norrlander undertook the time-consuming and expensive examination of the tooth. At first she did not think the item was even a tooth, but the more she looked, the more she thought it could be. She knew that under the conditions from which the tooth had been recovered, any DNA that might have been extracted from the tooth pulp would have been destroyed, so she had to resort to other methods. When she came across what appeared to be filling material, this confirmed it to be a human tooth and made it possible to determine if it might have been Katie's.

Tooth-fillings consist of an organic matrix and an inorganic filler material. The organic matrix burns off, leaving the filler particles behind. This allows an analyst to identify a brand or at least brand group. Manufacturers use as many as fifty different filler types, any of which will show up brightly on a dental x-ray. Once identified as dental filling, the elemental composition and microstructure can be studied for its classification, based on a distinct chemical signature. While this is still class evidence (indicating one of a group) rather than uniquely identifying evidence, it does allow investigators to narrow down possibilities. Katie could at least be eliminated if it did not match her dental work.

Katie Poirier
Katie Poirier
The composition of the filling of the tooth from Blom's fire pit matched that of the fillings used for Katie. In addition, researchers managed to identify it as tooth #18 and to determine that it was from a young female. The chance that it had once been in Katie's mouth rather than someone else from that area, was quite high.

While this type of analysis differs from the highly precise DNA probability estimates, and thus cannot deliver statements with such impressive mathematical calculations, it provides another level of certainty that investigators did not have before the analysis. Since they had few other physical clues, a lot would hang on it.

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