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How science helps unravel the most ingenious crimes

Sherlock Holmes and his deductive method definitely would have lost to modern forensics. Many promising technologies have replaced “old-fashioned” methods and helps to catch even the most sophisticated criminals. In this regard, the journal Science has decided to support scientists and revealed the latest achievements of the science of criminology that can make crime investigation objective. “Ribbon.ru” informs on the most promising technologies.

Voice and personality

In a notorious case, a voluntary patrol George Zimmerman, acquitted for the murder of black teenager Trayvon Martin, an important role could play a recording of the call 911 with sounds of screams. Who screamed — kill Martin (the prosecution) or Zimmermann, which a teenager was severely beaten? The acoustic experts found that the quality of the recording does not allow an unambiguous conclusion.

The problem is that the positive identification by voice is still not have a scientific basis. In the 1960s, analysts found similarities in the spectrograms (visualizations of the acoustic waves). But their subjective judgments on the basis of similar lines in the picture of the judge quickly recognized as quackery. In recent decades, specialists in signal processing create automated systems that measure the frequency spectrum of the speech every few milliseconds.

Operating a more traditional way, experts in phonetics break recording some sounds to find statistical regularities, but, ultimately, take decisions on their subjective feelings. Therefore, criminologists rely on objective, automated systems, with all their imperfections. Learn how alcohol intoxication, emotional state and type of a recording device affect the rhythm and tone of voice. Expert FBI voice recognition Hirotaka Nakasone says that such systems are used extensively in the course of the investigation, but the court did not recognize.

Microbial death watch

In a moment of death for billions of microbes begins his new life. Freed from the strict control of the immune system, they breed, multiply, trying to attack body tissue. Later they are joined by the bacteria from the external environment. Geneticist Jessica Metcalf (Jessica Metcalf) from the University of Colorado at boulder seeks to transform this dark process in a precision tool: a microbial clock to indicate the time of death more accurately than body temperature, muscle stiffness and insects.

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Forensics is collecting samples of soil around the rotting corpse


At the first stage of decomposition of a corpse devoured his most active cells of bacteria of the family Moraxellaceae, in particular, of the genus Acinetobacter. After them comes the turn of the representatives of the family Rhizobiaceae, are capable to incorporate biomass nitrogen. These microbes produce a multitude of gases that eventually tear the skin — inside the body gets oxygen, and power grab of the aerobic bacteria. Then begin to grow microscopic worms that feed on microbes.

Working with the corpses of mice, Metcalfe was able to determine the time of death with accuracy up to three days — three weeks after death. Then she and her colleagues took the corpse of a man on one of the so-called farm bodies, where criminologists study the process of decomposition. And again the dance of microbes served as a reliable tool: a month after the death of her point was determined with an accuracy of two days, the researchers note in the journal Science.

Hair as a track log

Hair analysis in forensics has earned a bad reputation. Previously, experts have tried to prove the presence of suspects at the crime scene, considering the color, thickness and curliness — however, the physical characteristics of hair, even under the microscope, too deceptive. Reconsideration of several high-profile cases of the 1970-ies revealed that the DNA of hair and the suspect is convicted based on this evidence I had to justify it.

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Forensic work with hair samples to the Punjab (Pakistan)

Photo: Zohra Bensemra / Reuters

The criminologists prefer to use the hair in the following ways. First, the keratin (the main substance of the scalp) contains all amino acids (21 a piece), but their ratio depends on the biochemistry of the body and has individual character. Therefore, the hydrolysis of amino acids gives a certain “profile” which indicate the sex, age, body mass index and even the origin of man.

Secondly, important information give the isotopes. It is known that isotopic ratios of hydrogen and oxygen in drinking water varies by region, and it is deposited in the hair that grew during the stay of the person in a particular place. For example, a private forensic company Isoforensics in 2008 found that an unknown woman (so-called “Sally of Soltera”), whose body was found in Utah in 2000, moved several times between Utah and North-Western areas in the U.S. shortly before his death. As a result, her personality identified by comparing with the list of women from these areas missing in 2000.

The microbiome as evidence

Forensics the University of Chicago several times faked the robbery of his colleagues. They took swabs from surfaces in the room (and door handles), looking for DNA and isolated one of its sections — the so-called 16S rDNA sequence that is unique for almost all types of bacteria. Removing from the data traces of the inhabitants of the house (people and cats), scientists are left with a mixture of microbial DNA thieves.

However, while this method (the identification of the microbiome) is in its infancy. Too many unknown factors: antibiotics and other medicines, even moving from one city to another, radically changing the composition of the microbial environment of a person.

Optimists also point to research 2015: scientists have measured the bacteria in the air around volunteers, placed in a disinfected room. The identity of several of them successfully installed on microbial cloud. In addition, the bacterial flora of a person is highly individual in nature, says peer Bork (Peer Bork), member of the European molecular biology laboratory (Heidelberg). In the first three or four years of life people are collecting from the environment a unique combination of bacteria and viruses, and it is more or less retained throughout life.

Of course, the most difficult to define this “mixture” for individual traces and fingerprints. According to Borca, one 16S rDNA technique is not enough here: you will need to sequence all the DNA from the crime scene and all the suspects microbiome — in order to identify even small differences between bacterial strains of the same species. In addition, you will need to create a universal database of individual microbiomes — at least several tens of millions of people. However, such a basis can be formed gradually, by analogy with the national list of fingerprints.

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Transcript of the Zimmerman call to the police

Photo: Joe Burbank / Reuters

The U.S. has already allocated one research group 900 thousand dollars on the development of a database on several tens of thousands of samples. Especially scientists interested in microbial “footprints” of bakers, farmers, and vegetarians. While even a minimal catch of 16S rDNA allowed the Chicago team to determine that one of the subjects had consumed at least 10 alcoholic drinks in the last week, and the other takes the pills from migraine headaches.

Confidence and statistics

The main problem of the science of criminology is not so much the imperfection of the methods, how much an adequate understanding of the limits of their capabilities. Unfortunately, too often in the twentieth century the authority of science was used by the prosecution to confirm questionable findings. In dozens of trials, the experts assured the jurors in the “uniqueness” of the results of forensic analysis. Few who took on the challenge to assess the real statistical probability of a match trace, fingerprints, and “trunk”. Only now, after the crisis of 2000-ies and the ongoing review of cases in the U.S., it is beginning to pay serious attention.

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