Murder “time travel”

  The body of a woman was found. The suspect revealed by the DNA actually died a few weeks before the woman. This is how the same thing?
  This is a real case, but it seems to come from a modern detective novel. In 1997, a woman was brutally murdered in London, England. The forensic doctor found tissue samples from other people under her nails, which may indicate that she grabbed the attacker before she died.
  One of the samples was tested, and the test results were entered into the British National DNA database for comparison, and a suspect was quickly compared. Surprisingly, this suspect was also a murdered woman, and she died three weeks before the death of the previous woman. They died in different areas of London, and their investigation teams were also different. Since there does not appear to be any connection between the two cases, and there is no evidence that the two women knew or met each other, the most “probable” situation is that their samples were mixed at first, and the location is most likely to be In a place where they have stayed-the British Forensic Services forensic laboratory. Therefore, the senior investigating officer filed a complaint.
  At that time, Silverman, a well-known forensic scientist and account manager of the British Forensic Services Department, was ordered to investigate whether the forensic laboratory made an error in this case. He first thought that it is possible that the nail cuttings of the second victim (the one who was killed later) were mislabeled, and these cuttings actually came from the first victim. But as soon as Silverman began investigating the relevant samples, he found that his speculation was wrong. The nails of the second victim had obvious leopard nail art patterns, and the nail shavings tested had exactly the same patterns. In other words, these nail chips must come from the second victim.
  Then, Silverman checked the laboratory records to see if it was possible that the samples of the two victims had been accidentally mixed. This was found to be impossible because the two sets of samples were not only placed separately, but also took out at different times. In any case, the nail cuttings of the two victims were tested a few weeks apart, and the inspectors were also different, so there is no possibility that the two cuttings samples will be confused in the laboratory.
  So, where is the problem? Silverman decided to investigate more closely how these nail chips were collected. He soon discovered that although the two bodies arrived at the morgue several weeks apart, they were subjected to an autopsy in the same morgue. Unlike standard non-criminal autopsy, forensic autopsy (autopsy) for murder or suspicious death is much more detailed and complicated. In addition to a variety of other tests, forensic autopsy also takes blood and organ samples of the deceased for toxicological examination, extracts stomach contents for examination, and scrapes and cuts nails for examination.
  When checking the records of the morgue, Silverman finally stopped. These records indicate that the body of the earlier murder victim was kept in a freezer for several weeks, during which time the police conducted an initial inspection. The day before the body of the second victim arrived at the morgue, the body of the first victim was removed from the freezer, allowing the pathologist to extract more nail chips. The next day, they used the same pair of scissors to extract the nail chips of the second victim. Silverman speculated that although the scissors were carefully cleaned between uses, it was still difficult to ensure that the cleaning process would eliminate any genetic material from the first victim from the scissors. In other words, it is entirely possible that the genetic material of the first victim will be transferred to the nail of the second victim through this pair of scissors, and a DNA profile will be generated in a later test.
  Silverman’s forensic career began in the late 1970s. At that time, the idea that a person can be identified from a few drops of blood seemed to come from science fiction. At that time, forensic scientists rarely wore protective clothing to enter the crime scene, and they rarely worried about potential contamination. The reason was that there was no way to detect any biological samples that were small enough to be visible to the naked eye, let alone detect DNA.
  Today, everyone who enters a crime scene must wear new protective clothing, overshoes and gloves. The current DNA extraction technology is so sensitive that even if it just touches an object (such as a doorknob or knife handle), it may leave enough traces for a successful DNA test. In 1997, when this “time travel” murder or “dead kills the living” case took place, DNA typing technology was only a few years away. But the technology has developed so rapidly that some previously unforeseen problems have followed.
  Silverman immediately arranged to inspect the nail clippers from the morgue, and found that there were three different DNA gene maps on the nail clippers. Further testing revealed that DNA contamination was also present on many other appliances in the morgue. However, this problem was only exposed in the nail clippers. For example, although DNA traces of multiple people have been found on the scalpel, since DNA is never extracted at the incision, cross-contamination is not intuitively reflected.
  Silverman immediately issued an emergency memorandum to all coroners, morgues and forensic pathologists in the UK, emphasizing the cross-contamination of forensic tools, and pointed out: From now on, all nail cuttings must be extracted in a single use Scissors, the scissors used must be put into the evidence bag containing nail shavings (extracted by this pair of scissors), make sure that the scissors have only been used this time. To this day, this rule is still being implemented in the UK.
  For many years, DNA has been regarded as the ultimate tool to fight crime with trace evidence, but in many ways, DNA testing has become a victim of its own great success. Forensic scientists have the ability to create a DNA profile with just a few human cells, and the necessary traces of evidence can be collected almost anywhere. But because we leave more or less DNA traces in all the places we have been to, the significance of discovering these DNAs and testing them will face more and more doubts unless there are enough materials on site. Eliminate secondary contact or cross contamination.
  DNA tests
  forensic scientists might be requested to compare the victims found the nail below the skin DNA, and DNA from blood suspected of suspects. First, isolate the DNA from the cell. A method called “polymerase chain reaction” (PCR) is used to make millions of copies of DNA. Use a natural enzyme PCR to replicate a specific segment of DNA repeatedly. Having a large amount of DNA makes it easier to detect genetic markers. Then, the DNA molecules are cut off at some specific parts, and the molecules are broken into “pieces.” Detect the code on the “block” and create a DNA fingerprint. Then compare the DNA fingerprints from two different samples to see if they match.
  How accurate is the DNA test? This question is very important, because DNA test results are sometimes the only evidence in an important case. The probability that two unrelated people have exactly the same genetic profile is less than one in a billion, so it is easy to see that the DNA from two biological samples does not match. But even if they match, it is not entirely certain that the two samples come from the same person. There is always a smaller possibility: two different people may have the same genetic markers, especially when they are related.
  To reduce errors, scientists will test more than one genetic marker. However, the more genetic markers tested, the more time and costly it takes. Forensic DNA testing usually examines 6-10 genetic markers.
  The case of DNA cracking
  In the 1950s, the American Anna became famous because she claimed to be the only survivor of the Russian Tsar, Grand Duke Anastasia. After Anna’s death, DNA testing proved that she had nothing to do with the Russian Tsar.
  The serial killer Spencer was the first criminal in the United States to be executed for DNA evidence. Vasquez was wrongly accused of killing a person in the Spencer series of cases. He was also the first person in the United States to be cleared of charges by DNA testing.
  In 1912, Dunbar, a 4-year-old American boy, disappeared while fishing with his family and was found eight months later. After he returned home, another woman claimed that he was her son. In 2004, DNA testing revealed that the boy was not Dunbar, and Dunbar’s whereabouts are still unknown. Some experts speculate that Dunbar fell into the lake and died, and his remains were eaten by crocodiles.