OCTOBER 17, 2008 -- Researchers at Baylor University (Waco, TX) have applied a statistical method to spectroscopy-based chemical measurements to determine the post-mortem interval of bones -- which is the time period since a person has died. The method is significantly faster than other forensicsmethods, and is effective for distinguishing short time intervals.
Because bones contain protein and water, the researchers chose a particular type of spectroscopy sensitive to moisture and protein. "When we thought about how we could determine the age of bones, we thought that when bones die, they may begin to dry out, and that the protein might start to decompose and break apart," said Dr. Kenneth Busch, professor of chemistry and a lead researcher for the project. "So then we thought we could use spectroscopy to follow that process."
Through regression modeling, Busch and fellow researchers were able to correlate their data with the post-mortem interval. "In this case, we shine light on a bone and measure how much it reflects back," Busch said. "We found that the signal from our instrument did change as a function of time, and were able to correlate that change with a time interval -- the post-mortem interval, which ultimately tells how long it has been since a bone has died."
This method, diffuse reflectance spectroscopy, was tested on 28 different pig bones.
"We do it over a certain set of wavelengths, then take all the data from our instrument and put it in a statistics program and analyze it in various ways," said Patricia Diamond, graduate student of chemistry and fellow researcher. "No one is doing the spectroscopic work we've done." Diamond said other researchers tend to look at various elements of carbon and nitrogen, and also at larger age ranges of bones.
"We are trying to look at a lot smaller age ranges," she said. "We haven't looked at anything over a year old. We are hoping that spectroscopically we can take some bones that are only separated by a few weeks and tell the difference between them."
Determining the age of very old and very young bones isn't as much of a challenge as determining the age of bones that fall in between.
"There is a sort of in between time period in which it's difficult to pinpoint the date of death," said Dr. Marianna Busch, professor of chemistry and biochemistry and Dr. Kenneth Busch's wife. "Hopefully our technique will provide a method for these bones that fall in the middle range."
The Baylor researchers are targeting forensics, not archaeology.
"We're looking at a situation where the bones haven't been there for hundreds of years, but for shorter intervals," Dr. Kenneth Busch said. "In any criminal investigation, the police need to establish when the person was last alive. That's why our research is important."
There was an error rate of only four to nine days for 90-day-old and younger bones when the researchers tested the method of estimating age.
"Our method isn't absolute -- we can just give a range -- but once a regression model is built, the time it takes to determine the age of a bone is cut down significantly," Dr. Kenneth Busch said. "Our hypothesis was correct in the sense that we were able to correlate our spectrum with a time interval. Regardless of whether this really has to do with the moisture and protein in the bones, we don't know. But that's kind of the fun of science."
Adapted from materials written by Baylor University.