Tag Archives: forensic

Fallible Fingerprints

Posted on March 20, 2019 by | 3 comments

Before DNA evidence became the golden standard for forensic labs, convicting a criminal often meant dusting the crime scene for prints.

All forensic evidence are liable to error and fingerprints are no exception. In general, there are two types of error: false negative and false positive. A false negative occurs when the two fingerprints are a match but the examiner declares the fingerprints to be different. A false positive is when two fingerprints are not a match but the examiner concluded otherwise. In both cases the consequences are different, while false negatives may not entirely exonerate a criminal, false positives can lead to wrongful convictions where an innocent person can face jail time for something they did not do.

Example of a fingerprint Source: Wikimedia Commons

There are eight common fingerprint patterns: arches, tented arches, right loops, left loops, plain whorls, central pocket loops and double loops. When the lines or ridges on a finger develops and meets other ridges, the two ridges can interact in many ways, resulting in what is called a minutiae. Since fingerprints depend both on genetic and environmental factors, the patterns developed are very unique. Even identical twins can develop different fingerprints. However, theory and practice can be very different. In the modern age, there still is not a definitive certainty in how unique the match between fingerprints are. It was claimed that a false positive was one in 64 million. In one study, researchers found fingerprint exams had a false positive error rate of 0.1% and a false negative rate of 7.5%. These numbers show that human error and the quality of fingerprints can significantly influence how forensic experts perceive the evidence.

In the famous case of the Madrid train bombings, Brandon Mayfield was wrongfully convicted based on fingerprints that were found at the scene due to poor quality of the fingerprints. Later on, when the five fingerprint experts were asked to re-examine these prints, three experts reversed their conclusion and claimed the results were inconclusive. In conclusion, while fingerprints are a useful tool, they are not infallible and prone to human error more than one expects.

(1)
Knapton, S. Why Your Fingerprints May Not Be Unique. The Telegraph. March 14, 2016.
(2)
The “CSI Effect.” The Economist. April 22, 2010.
(3)
Statement on Brandon Mayfield Case https://www.fbi.gov/news/pressrel/press-releases/statement-on-brandon-mayfield-case (accessed Mar 20, 2019).
(4)
Latent Print Examination and Human Factors: Improving the Practice through a Systems Approach. 249.
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Latent Print Examination and Human Factors Improv.Pdf.
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God’s signature: DNA profiling, the new gold standard in forensic science. – PubMed – NCBI https://www.ncbi.nlm.nih.gov/pubmed/12798816 (accessed Mar 20, 2019).
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Stephanie. False Positive and False Negative: Definition and Examples https://www.statisticshowto.datasciencecentral.com/false-positive-definition-and-examples/ (accessed Mar 20, 2019).
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Photographer, T. English: Fingerprint; 2009.
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Spiro, R. Do Identical Twins Have Identical Fingerprints? | Washington State Twin Registry | Washington State University. Washington State Twin Registry, 2015.
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14 Amazing Forensic Science Techniques.
(11)
8 Most Common Fingerprint Patterns. Touch N Go, 2017.

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Posted in Issues in Science

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Forensic: How to Measure the Unknown Time of Death from Only Bone and Hair Remains

Typically, TV forensic shows, such as CSI and Bones, portray how forensic cases are fast and easy to solve within a couple of episodes. However, that is not true. Unlike in forensic shows, forensic cases take a long time to solve in real life, due to challenges that investigators have to face.

One of the challenges that criminal investigators have to solve is to determine the post-mortem interval (PMI) from decomposed skeletons. Post-mortem interval is the time after someone has died, which is important when the cause of death is unknown. Usually, medical assessment of corpses can determine the PMI after the body is dead for the first few days. However, when the victim’s bones and hairs are found after a few years, the accuracy of the PMI lowers. Therefore, new method is required to provide a more accurate estimation of the extended time of death.

Currently, there are numerous studies that use different methods for solving the PMI. Many methods include analyzing soil chemistry and insects at the crime scene. Since these methods could be complementary to each other, the scientists in Switzerland believe that combining these methods would improve the long-term PMI estimate, while illustrating how the crime scene could have occurred. Therefore, the Swiss scientists have attempted to use five different approaches simultaneously to estimate the PMI of the bone and hair remains. Once the soil, bone, and hair samples are collected from the Swiss forest, the scientists use five different approaches for analyses, which include using radiocarbon dating, analyzing pH and soil chemistry, counting and classifying nematodes and mites, and sequencing DNA of soil micro-eukaryotes.

 

After analyzing the findings, the scientists are able to propose a possible PMI, as well as the crime scene. First of all, the radiocarbon dating determines that the bones belong to a young adult male. Secondly, chemical, nematodes, and micro-eukaryotic analyses suggest that the remains have been partly decomposed in the forest for at least 8-9 months. Finally, the evidence from mites suggests that the corpse is partly decomposed in a separate confined place, because these mite species are only found in confined environment. Therefore, the suspect(s) could have allowed the corpse to decompose in a confined area before relocating it to the Swiss forest. As a result, the PMI of the dead victim appears to be at least 8-12 months before the body is discovered.

The skeleton that is found in a Swiss forest. Ildikó Szelecz, Sandra Lösch, Christophe V. W. Seppey, Enrique Lara, David Singer, Franziska Sorge1, Joelle Tschui, M. Alejandra Perotti & Edward A. D. Mitchell, Source, Creative Commons Attribution 4.0 International Licence

Overall, the study shows that using five approaches simultaneously in a forensic case study can estimate the PMI, while illustrating a possible crime scene of how the victim could have died. Moreover, all of the approaches can be complementary with each other, in order to provide more evidence from scarce remains. In conclusion, it is possible to further develop this technique in order to estimate PMI in other forensic cases.

Update: Blog post has been revised on 2019, Feb 15th.

Reference

Rasmussen College. How Accurate are Crime Shows on TV? Debunking 7 Common Myths. https://www.rasmussen.edu/degrees/justice-studies/blog/crime-show-myths-debunked-forensic-experts-tell-what-life-is-real/

Keele University. Chemical Ecology. PMI in Forensic Entomology. https://www.keele.ac.uk/chemicalecology/projects/pmi/

American Council on Science and Health. How Chemistry, Microbiology Could Help Catch A Killer. https://www.acsh.org/news/2018/01/18/how-chemistry-microbiology-could-help-catch-killer-12422 .

Szelecz, I.; Lösch, S.; Seppey, C. V. W.; Lara, E.; Singer, D.; Sorge, F.; . . . Mitchell, E. A. D. . Comparative analysis of bones, mites, soil chemistry, nematodes and soil micro-eukaryotes from a suspected homicide to estimate the post-mortem interval. Scientific Reports. [Online] 2018, 8(1), 25. doi:10.1038/s41598-017-18179-z.

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Posted on January 29, 2019 by in Biological Sciences, Science in the News, Uncategorized

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