Category Archives: Crime Scene

Forensic Evidence Errors in Arson Investigations and Crime Scene Processing

Paul Bieber (Director at Arson Research Project: http://thearsonproject.org/research/) explores the misidentification of an accidental fire as an act of arson and how unreliable, quasi-scientific techniques led to the mistaken execution of an innocent man. On June 30th, join the UNC School of Government and the North Carolina Office of Indigent Defense Services for the seventh installation in the Evenings at the School of Government series, Beyond Willingham: Recognizing Errors and Crafting Solutions in Fire Investigations. The program provides one and a half (1.5) CLE credit hours and is designed to enhance the knowledge of all criminal law practitioners, not only in understanding the investigative techniques used, but in raising challenges to that evidence.

Location, Date, and Time: Thursday, June 30th, 2016 at the UNC School of Government room 2603. Sign-in begins at 5:15pm, the program begins at 5:30pm, and is set to conclude by 7:00pm.

RSVP: Registration is not required, but we ask that you RSVP via email to Monica Yelverton, at myelverton@sog.unc.edu.

Materials: Materials for this program are forthcoming and will be available on the program website http://www.sog.unc.edu/courses/evenings-school-government under the materials tab. Those who RSVP for this event will receive a confirmation email on June 23, 2016 with a link to the program materials. Please note that the materials will not be provided in hard-copy form at the program. We recommend that you either bring a laptop to access the materials electronically or bring a hardcopy.

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New Research on “Touch” DNA

As the sensitivity of DNA analysis increases, scientists are able to develop profiles from ever-smaller samples of DNA. This has lead to testing of a wider array of samples collected from crime scenes, including window panes, bullets, hats and other clothing, cigarette butts, and many other items.

Attorneys sometimes ask me about the likelihood of obtaining a useful DNA profile from certain items of evidence. A study from six European forensic laboratories may give some idea of how likely it is to find a DNA profile on items commonly found at crime scenes. This article contains an interesting chart that lists the item and the likelihood of finding a full profile, usable partial profile, possibly usable partial profile, or no profile. It seems best to use this type of information as a rough guide, but it is interesting nonetheless.

It is important to keep in mind that as labs are able to analyze smaller amounts of DNA, the possibility of developing partial profiles and complex DNA mixtures increases. Where very small amounts of DNA are involved, the sample may have been deposited by secondary transfer. Here’s an interesting article on secondary transfer and “touch” DNA.

Attorneys should be aware that forensic laboratories may have case submission guidelines that limit the number and type of items that may be tested by the lab. To understand why and how an item was tested (or not), it is important to read the lab’s policies and guidelines. Here is a link to the North Carolina State Crime Lab’s Evidence Guide. There is information about Touch DNA testing on p. 52.

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Cognitive Bias and Forensic Anthropology

A study looking at how the conclusions of forensic anthropologists may be influenced by extraneous information highlights the importance of protecting all scientists from potentially biasing information.

Forensic anthropologists determine the gender, national origin, and age of a person at the time of death. In some cases this determination must be based solely on skeletal remains. A recent study introduced extraneous information to the scientists when remains were submitted for scientific analysis and found that background information can bias a scientist’s conclusions and result in mis-identifications across the board.

In this study, three test groups were assembled to analyze the remains of a nineteenth century female skeleton with strikingly neutral, or “ambiguous,” features which could allow a conclusion of either sex. An ambiguous environment is one that creates the greatest potential for cognitive bias. Cognitive bias occurs when contextual information influences a person’s thought process and may lead to inaccurate judgment. In this case, scientists relied on information that was submitted with the evidence, causing them to make conclusions validating or complementing the extraneous information.

Two of the three groups were given DNA profiles in addition to skeletal remains. The first group’s DNA profile indicated the skeletal remains belonged to a Caucasian male between 25-30 years of age. The second group was given a DNA profile indicating the same skeleton was an Asian female between 50-55 years of age. The third group, the control group, was given no supplementary information. Each scientist, ranging from master’s degree students to practicing PhDs in anthropology, was given up to an hour to examine the remains and make conclusions. In the first group, 72% concluded the remains were male and 100% of examiners in the second group concluded the remains were female. In the control group 31% of examiners concluded the remains were male and 69% concluded female.

Regarding ancestry, 100% of group one (who were told the skeleton was Caucasian) and 100% of the control group (who were given no extra information) decided that the skeleton was Caucasian. In group two, where the scientists were told the skeleton was of Asian ancestry, 50% concluded the skeleton was of Asian descent and 50% concluded Caucasian. The study attributes the bias in both group one and the control group to cognitive bias and bias generated from ancestrally-common characteristics described in anthropological textbooks.

This study showed that age at time of death is the least affected category by cognitive bias. Anthropologists in each group reached conclusions about age independent of the supplied information.

This study shows how biasing contextual information can affect a scientist’s ability to be impartial. The accuracy and credibility of a scientist’s conclusions depends upon blinding the scientist to any information that can be consciously or unconsciously biasing. Attorneys may be interested in reading similar studies that have looked at how contextual information can bias examiners in the fields of blood spatter interpretation, fingerprint comparison, and DNA interpretation.

 

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New research on how vultures affect time of death determinations

Researchers at Texas State University’s forensic anthropology research facility, one of the country’s five “body farms,” have discovered that failure to take into account the role of vultures may have affected time of death calculations in homicide investigations. See Associated Press coverage here.

The scientists observed a flock of vultures reduce a corpse that had been laying in a field on the body farm for 37 days to skeletal remains within hours. The resulting absence of flesh and condition of the bones normally would lead investigators to conclude that the person had been dead for six months or longer. These observations call into question previous techniques for determining time of death that did not take the role of vultures into account. Additional research is on the role of vultures is planned.

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Crime Scene Investigation – New Website

As a follow-up to my post from earlier this week on crime scene investigation, I have created a website with articles and publications that describe best practices for physical evidence recognition, evidence preservation and collection, and crime scene documentation. I have posted standards and guidelines for crime scene investigation and other crime scene resources on this new page in the Indigent Defense Services forensics website, available here.

If you have feedback on the website or additional materials you’d like to see included, please send me an email or post a comment on the blog.

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