Everything Worth Knowing About … Catching a Criminal

Everything Worth Knowing About … Catching a Criminal

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In 13th-century China, a field worker was killed with a sickle — and all villagers’ sickles were alike. So the investigator had every worker lay down his tool in a field, and observed that just one sickle attracted blowflies, which were known to seek out blood. Its owner, the culprit, immediately confessed.

The Chinese sickle slaying is one of the first reported cases of forensic investigation. The role of science in evidence collection and presentation has only become more important over time, and it continues to evolve at an ever-accelerating pace.

New discoveries are bolstering even the oldest techniques, such as fingerprinting, first systematized by Englishman Sir Francis Galton in 1892. For instance, in 2015, National Institute of Standards and Technology chemist Shin Muramoto found that ridges on a fingerprint release a substance known as palmitic acid at a predictable rate, allowing investigators to determine when prints were laid down and whether they’re temporally relevant to a crime. And at the University of Albany, chemist Jan Halámek recently published a method to determine the sex of the person who left a print based on proportions of amino acids found in skin oils.

One of the most significant developments in forensics — the advent of DNA profiling in the 1980s — also continues to advance. More than just a means of tying a suspect to a crime scene, genetic information can reveal clues about a culprit’s appearance through a process called DNA phenotyping. Indiana University-Purdue University Indianapolis geneticist Susan Walsh has successfully predicted eye and hair color based on genetic markers known as single nucleotide polymorphisms (SNPs), and Pennsylvania State University anthropologist Mark Shriver has used SNPs to make predictive digital mugshots.

DNA phenotyping has met some skepticism, which is important given an individual’s freedom may be on the line; overconfidence and pseudoscience both have a long and tragic history in forensics. Exhibit A: Galton, the father of fingerprinting, falsely claimed that criminal tendencies could be detected in the faces of people who physically resembled known lawbreakers. Last year, a study released by the President’s Council of Advisors on Science and Technology raised a fresh round of concerns, finding inadequate scientific support for standard techniques ranging from ballistics testing to blood spatter analysis.

However, forensic science is also a powerful technique to scrutinize itself, as researchers discover and correct past inadequacies. Studying the reasons why blood spatter can be misleading, Loyola University Maryland biologist David Rivers recently observed that the blood was sometimes spread by flies. So in a move that would surely have impressed medieval China’s CSI, Rivers developed a spray that could distinguish bug-borne spatter by detecting fly gut enzymes in bloodstains.

Check out some other cutting-edge ways researchers are advancing established investigation methods.

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