The impeccable DNA detection technology, why do you frequently create false and wrong cases?

Release date: 2016-07-21

In many people's eyes, DNA detection technology is simply the ultimate artifact. Every time the case goes to the end of the mountain, a hair, a drop of blood, a little body fluid... But if you can bring a little bit of biological information, these seemingly inconspicuous evidence can be turned into a magical, open the crowd, pointing to the murderer .

But the question is: How reliable is DNA detection technology? Doesn't it make mistakes?

[The case under the "Iron Certificate"]

Carol Batti, a citizen of Houston, USA, had hoped that DNA testing technology could prove the innocence of his son Josiah Sutton, but the result was counterproductive.

In 1998, 16-year-old Sutton and neighbor Gregory Adams walked down the street and were referred to by a rape victim as the murderer. Both of them had proof of absence at the time of the incident and the body was very different from the victim’s description to the police at first. They hope that DNA technology can prove their innocence and agree to blood tests.

Christie King, an analyst at the Criminal Investigation Laboratory of the police station, after extracting DNA samples from the two and the victim, ruled out Adams’ suspicion of the crime, but determined that the Sutton DNA was “consistent” with the victim’s vaginal swab collection. Soon, Sutton was sentenced to 25 years in prison for rape.

Batty asked for help from his son, but many lawyers refused to take over when they heard that the evidence involved DNA. It was not until four years later that she accidentally saw a survey program on the local TV station and rekindled hope.

According to this program, the Houston Police Criminal Investigation Laboratory, one of the leading public health centers in Texas, handles at least 500 cases of DNA evidence each year. According to the informant's report, the program team gave dozens of DNA maps of the laboratory to third-party experts for analysis, and found that police technicians often made mistakes even the most basic samples.

"If this can be incompetent," William Thompson, a professor of criminology at the University of California, Irvine, commented, "They are seriously incompetent, and they are seriously and again and again."

After the program was broadcast, many people called the program group to talk about their experience of DNA detection. Sutton is one of the imprisoned. After the show group introduced Bhatti to Thompson, he and his wife, who are lawyers, found doubts from the two boxes of interrogation materials: To build a reliable DNA map for a person, the analyst needs to collect samples from multiple parts of the body. The DNA characteristics extracted from each sample should be identical. However, the data show that gold is very different from the DNA extracted from the victim's blood and a saliva.

Thompson said that if technician Jin did not get a consistent DNA fragment from the same person, how can she expect her to correctly distinguish individual DNA from vaginal swab collections that may have three human gene fragments? More importantly, according to the gold test, Sutton's DNA did not match the genetic markers extracted from the semen samples. The evidence is enough to prove that the boy is innocent, but "no one told the judge about the matter in the past."

Soon, Batty found a new lawyer, Sutton regained freedom, the real rapist was arrested in another case in 2006, and Kim was fired. But her lawyer said that this is not the fault of Kim, it is the failure of the entire system, such as poor supervision.

In 2014, the City of Houston shut down the Criminal Investigation Laboratory and handed over the business to the newly established independent accreditation body, the Houston Forensic Center, to ensure the independence of the accreditation body. But for Batti, everything is late. The son turned into a street gangster from the ruthless rugby player, and is currently being beaten for trial. When the reporter asked her if she blamed DNA technology, she replied: "No. DNA is science, you can't blame it. You can only blame those who use it wrong."

Thompson said that many cases have proved that his years of worry about the risk of DNA testing is not a worry. In fact, "this is no longer a question of whether or not there is a possibility of making mistakes, but a question of how many mistakes have been made and how we should correct them."

[How is superstition developed? 】

DNA detection technology originated in academia, based on human genetics, with a strong "scientific" aura, many people believe that it can eliminate subjective interference to the utmost. "Compared to DNA technology, other forensic methods are not so accurate, reliable, and highly positive that evidence is linked to a specific individual or source," the National Research Council said.

The genetic fingerprinting technology developed by British geneticist Alec Jeffries in 1986 was used for criminal investigations for the first time, helping the police to detect unsolved cases and catching the real murderer. The forensic identification technology has ushered in a new era.

Carnegie Mellon University professor Jay Aaronson said that DNA detection technology was also interfered with when it first entered the United States. Some defense lawyers thought it was not enough to prove that it did not pass the Frye test. When this test standard requires the adoption of scientific evidence, the principles and methods relied on by expert testimony must be generally accepted by the field in which it belongs; some well-known universities complain that commercial test institutions are intimate and transparent to specific technologies. These controversial issues have all been "satisfactoryly resolved".

Nowadays, DNA detection technology is constantly improving. The FBI has established a powerful DNA Synchronization System (CODIS) and has given a large number of private laboratory-related qualifications to seek to standardize sample collection and storage procedures. People are increasingly convinced of its reliability.

Lawyers Barry Scheke and Peter Neufeld used DNA detection and analysis techniques as weapons to counter the defendants who believed they were victims of racial discrimination. So far, the two won 178 appeals, the majority of whom were black. In their eyes, when defense lawyers and prosecutors are derelict, "DNA testing can lead to justice and become a way to restore the truth."

The greater role of DNA technology is to help the police find the real murderer. The number of criminal investigation laboratories in various states, counties, and municipalities in the United States has doubled, and more and more cases have been applied for the detection of DNA evidence. In 2000, the FBI DNA Joint Search System was established just two years ago, with less than 500,000 copies of DNA maps and about 1,600 criminal cases assisted in investigations. As of 2015, the system has stored more than 15 million DNA maps and assisted in the investigation of tens of thousands of cases last year alone.

Nowadays, with the popularization of the Criminal Investigation Bureau such as the Crime Scene Investigation, the authority of DNA evidence has become more and more popular. When Michigan State Judge Donald Shelton randomly surveyed more than 1,000 jurors in Ann Arbor in 2008, three-quarters of them wanted the prosecution to provide DNA evidence in rape, and nearly half wanted evidence in murder. DNA appears in 22%, and hopes to provide DNA evidence in every criminal case.

Australian researchers have found that in sexual assault cases, the existence of DNA evidence doubles the likelihood of trials and 32 times the likelihood of a defendant's conviction; in the murder case, the likelihood of trials for DNA is 13 times greater. The probability of conviction increased by 22 times. The Nafield Bioethics Association of the United Kingdom said that merely referring to the prosecution’s intention to introduce a DNA comparison is enough to shock the defendant to plead guilty on the spot.

“The current situation is that people almost never discuss (DNA) sampling, analysis and preservation issues,” said San Francisco Baro, a San Francisco lawyer who has been dealing with DNA evidence for 20 years. “DNA evidence is hard to overthrow. In most cases. For many lawyers, it is too expensive and too time-consuming to do with DNA."

[What is the frequency of the error? 】

Why does the seemingly invulnerable DNA detection technology frequently create false and wrong cases?

Experts point out that 99.9% of human genes are completely identical, and only by identifying as many special alleles as possible can the scope be precisely narrowed down to an individual, which is why Jeffries emphasized the need to introduce this technology in criminal cases. Large sampling, comparison testing, and repeated confirmation.

According to the current US identification laboratory standards, analysts usually compare the 13 loci alleles to determine whether two individual samples are from the same person, because the probability that these genes are identical in two people is less than one billion. One of the points. But if a sample involves two people, the number of alleles that need to be aligned is doubled; if three people are involved, the logarithm is doubled; and so on. It is difficult to understand the specific factors involved and the differences. Once the sample is too small or damaged, such as the handshake caused by gene overlap, etc., it may cause the allele to be missing or appear in the place where it does not exist. How to identify it becomes a subjective thing.

Idrier Drol, a cognitive neuroscientist at the University College London, and Greg Hampichia, a professor of biology at the University of Boise, USA, have conducted research. They received a rape case in 2010, and the key to solving the case depends on the DNA typing results. One of the accused was sentenced to a reduced sentence and the accomplices were convicted. At that time, the two forensic doctors concluded that the semen mixture extracted from the victim could not rule out the possibility of the colleague committing the crime, and the associate was eventually found guilty. Drol and Ham Pikia handed the DNA evidence to 17 senior laboratories for testing. They did not introduce the details of the case and only asked them to determine whether the DNA of the associate was included in the semen. As a result, only one laboratory thought that semen might contain his DNA, another 12 excluded his suspicion, and four said it could not be determined.

Drol and Ham Pikia quoted a predecessor at the end of the report and wrote that in order to confirm the identity of a person from a mixed multi-person gene, "10 experts can have 10 different conclusions. ".

Ellen Murphy, a professor of law at New York University, said that DNA detection technology was originally intended to eliminate subjective interference. However, the more she studied, the more she found that subjectivity still existed.

Murphy published a book last year to review the case of DNA typing errors, and concluded that there are two reasons for the error. First, the sample is contaminated or exchanged during sampling or analysis. A black boy in Nevada was arrested for eight years in prison because the police mistakenly sent his DNA as a sample of the crime to the laboratory. When the American football star OJ Simpson was suspected of murdering his wife, his defense lawyer Helping him offend with a critical DNA evidence that was contaminated during collection. The second is DNA transfer, that is, the transfer of cellular genetic material between different individuals and between individuals and objects. When we come into contact with people or things, talk or even wash clothes, it is inevitable that DNA transfer will occur and it is difficult to trace. Since the number of cells that are shed by each person is different, the clearest DNA profile on an object does not necessarily come from the last person who touched the object.

Murphy said that if you take careful care when sampling, you can minimize the contamination of the sample, but DNA transfer is almost inevitable. What is worrying is that many laboratories are now pursuing the extraction of genetic information from as little evidence and sample as possible. This technique appears to be cutting-edge, but is more likely to contaminate samples or lose alleles and create defamation cases.

Murphy finally wrote in the book that there are no authoritative figures showing how many people have been accused or even imprisoned for errors in DNA evidence. However, "this flawed criminal trial system does not reflect on even the wrong case, but now it has added a powerful weapon to its arsenal."

Source: Xinhua News Agency

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