Published in 2018 by
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Designer: Deanna Paternostro Editor: Jennifer Lombardo
Library of Congress Cataloging-in-Publication Data
Names: Jennings, Cecilia, author.
Title: DNA evidence : the proof is in the genes / Cecilia Jennings.
Description: New York : Lucent Press, [2018] | Series: Crime scene investigations | Includes bibliographical references and index.
Identifiers: LCCN 2017044918| ISBN 9781534561762 (library bound book) | ISBN 9781534562738 (paperback book) | ISBN 9781534561755 (eBook)
Subjects: LCSH: DNA fingerprinting. | DNA-Analysis. | Forensic genetics-Technique. | Evidence, Criminal.
Classification: LCC RA1057.55 .J46 2018 | DDC 614/.1-dc23 LC record available at https://lccn.loc.gov/2017044918
Printed in the United States of America
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Introduction:
Crime Scene Science
Chapter One:
The Early Days of DNA
Chapter Two:
How to Build a DNA Profile
Chapter Three:
A Brief History of DNA Profiling
Chapter Four:
Beyond Crime Scenes
Chapter Five:
A Darker Side of DNA
For decades, popular television programs and movies have depicted the life and work of police officers, detectives, and crime scene investigators. Many of these shows and films portray forensic scientists as the brains responsible for cracking cases and bringing criminals to justice. Undoubtedly, these crime scene analysts are an important part in the process of crime solving. With modern technology and advances in forensic analysis, these highly trained experts are a crucial component of law enforcement systems all across the world.
Police officers and detectives are also integral members of the law enforcement team. They are the ones who respond to 911 calls about crime, collect physical evidence, and use their high level of training to identify suspects and culprits. They work right alongside forensic investigators to figure out the mysteries behind why a crime is committed, and the entire team cooperates to gather enough evidence to convict someone in a court of law.
Ever since the first laws were recorded, crime scene investigation has been handled in roughly the same way. An authority is informed that a crime has been committed; someone looks around the crime scene and interviews potential witnesses; suspects are identified based on evidence and testimony; and, finally, someone is formally accused of committing a crime. This basic plan is generally effective, and criminals are often caught and brought to justice. Throughout history, however, certain limitations have sometimes prevented authorities from finding out who was responsible for a crime.
There are many reasons why a crime goes unsolved: Maybe a dead body was found too late, evidence was tampered with, or witnesses lied. Sometimes, even the greatest technology of the age is simply not good enough to process and analyze the evidence at a crime scene. In the United States during the 20th century, for example, the person responsible for the infamous Zodiac killings was never found, despite the earnest efforts of hundreds of policemen, detectives, and forensic analysts.
In modern times, science and technology are integral to the investigative process. From DNA analysis to high-definition surveillance video, it has become much more difficult to commit a crime and get away with it. Using advanced computers and immense databases, microscopic skin cells from a crime scene can be collected and then analyzed by a forensic scientist, leading detectives to the home of the culprit of a crime. Dozens of people work behind the scenes of criminal investigations to figure out the unique and complex elements of a crime. Although this process is still time-consuming and complicated, technology is constantly improving and adapting to the needs of police forces worldwide.
This series is designed to help young readers understand the systems in place to allow forensic professionals to do their jobs. Covering a wide range of topics, from the assassination of President John F. Kennedy to 21st-century cybercriminals, these titles describe in detail the ways in which technology and criminal investigations have evolved over more than 50 years. They cite eyewitnesses and experts in order to give a detailed and nuanced picture of the difficult task of rooting out criminals. Although television shows and movies add drama to the crime scene investigation process, these real-life stories have enough drama on their own. This series sticks to the facts surrounding some of the highest-profile criminal cases of the modern era and the people who work to solve them and other crimes every day.
Although crime-solving work is a lot more than simply matching suspects to deoxyribonucleic acid (DNA), it is true that DNA can be useful to detectives when they are trying to prove someone’s involvement in a crime. Because DNA is unique in every individual, it can be thought of as the genetic blueprint of humans and other living things—indeed, DNA is sometimes referred to as the “genetic fingerprint.” Just like someone’s fingerprints can prove that they touched or handled a certain object, DNA can be used to place a suspect at the scene of a crime—or prove they were not there. This process is sometimes called DNA fingerprinting, even though it does not involve actual fingerprints. More commonly, it is called DNA analysis.
Modern television crime dramas have helped make the public aware that DNA analysis is part of a special branch of science called forensic science, often simply called “forensics.” Forensics applies scientific methods to legal matters, particularly to solving crimes. DNA is not the only form of evidence used in the fascinating world of forensic science. The forensic experts depicted on CSI: Crime Scene Investigation,often referred to as just CSI, and other shows regularly supplement their DNA analysis by examining finger and palm prints, shoe and tire tracks, blood types, cloth fibers, and many other kinds of forensic evidence.
The use of DNA analysis as a scientific crime-solving technique became available to law enforcement officials only in the last few decades, as technology evolved to allow investigators to collect and analyze samples left behind at crime scenes. The forensic use of DNA is the result of a long, winding, often uneven history of scientific crime solving. Like all areas of scientific inquiry, DNA’s use in criminal investigations would not have happened without many years of study. In fact, widespread understanding of forensic methods did not exist until about a century ago. However, police and other investigators have attempted to solve crimes throughout recorded human history, and basic scientific tech-niques—although not yet called “science” or “forensics”—were introduced into the process a little at a time over the centuries.
The first known use of forensics to solve a murder case occurred in China, sometime before 1248. This is known thanks to Chinese writer Song Ci, who compiled a book titled Collected Cases of Injustice Rectified. The volume told about various investigations by doctors and other authorities into people’s deaths to make sure justice had been served. In one important case, a man had been murdered with a farm tool called a sickle. In an effort to find the guilty party, the investigator asked each villager who owned a sickle to bring it to him. After a while, flies began to gather on one particular sickle. The investigator reasoned that the flies were attracted to traces of blood left on the blade after the killer had wiped it off. They were able to get a confession from the sickle’s owner and thereby solve the murder. Today, an investigator might conduct an investigation much the same way, but rather than using flies, they would test each blade for traces of DNA and compare them to the DNA of the victim.
Centuries after Song Ci reported on the use of flies to detect blood residue, various other forensic techniques began to develop in Europe. An early example is the 1816 murder of a young woman in Warwick, England. A police investigator found grains of wheat, boot prints, and the impression of a certain kind of cloth in the soft earth near the body. He then matched these impressions with the trousers of a farm laborer who lived nearby and had been threshing the wheat near the crime scene, solving the case. The investigator’s careful examination of the crime scene allowed him to spot key pieces of evidence the killer had left behind—much the way that, centuries later, police and forensic scientists would analyze a crime scene for traces of DNA.
Inspired by early investigators, in the mid-1800s, a young English doctor named Alfred Swaine Taylor began teaching forensic medicine in London, England. He was the first researcher to support a careful examination of all evidence at a crime scene by a trained medical expert. In a way, this marked the birth of the modern crime scene investigator (CSI). Taylor wrote,
A medical man, when he sees a dead body, should notice everything. He should observe everything which could throw a light on the production of wounds or other injuries found upon it. It should not be left to a policeman to say whether there were any marks of blood on the dress or on the hands of the deceased, or on the furniture of the room. The dress of the deceased as well as the body should always be closely examined on the spot by a medical man .1
The “medical man” Taylor mentioned is a combination of today’s medical examiner and CSI unit. It is the CSI unit’s job to meticulously, or carefully, document everything at the scene, take samples of anything they think might be useful—hair, blood, fingerprints, and more—and bring it back to the lab to be analyzed. The medical examiner, if onsite, goes over the crime scene with a physician’s eye and examines the body to determine the cause and pronounced time of death. The pronounced time of death is the time at which the person is declared dead by law enforcement or medical personnel.
Forensic investigators and analysts who create DNA profiles are often asked how the reality of their work compares to the stylized drama of the increasingly popular genre of police procedural TV shows, such as CSI and Bones. One major difference the real CSIs cite is that in real crime investigations, the investigators who collect evidence at crime scenes generally do not interview witnesses and chase down criminals, and investigators do not analyze the samples that the CSI unit collects at the crime scene. That task is carried out by trained analysts who generally remain in the lab, analyzing and processing evidence from many sources at once.
TV dramas also show DNA analysis happening much faster and easier than it does in real life. Moreover, due to budgetary restraints, most real-life crime labs are understaffed and underfunded, resulting in large backlogs of work, which makes solving crimes an even slower process. In fact, there are currently tens of thousands, possibly hundreds of thousands, of sexual assault evidence kits—the samples taken from women who report that they have been raped—sitting untested in crime labs and at police storage facilities. Some labs are trying to fix this by hiring more workers and using new technology, such as robots that can analyze DNA faster than a human can.
Only a few trained experts knew about and understood the principles advocated by Taylor; the general public was unaware of them. That changed rather abruptly in the late 1800s, however, thanks to a talented Scottish mystery writer named Sir Arthur Conan Doyle. Between 1887 and 1927, Conan Doyle wrote several stories and books featuring the world’s most famous fictional detective: Sherlock Holmes.
Conan Doyle based the character on one of his college professors, Dr. Joseph Bell, who—along with Taylor—was a pioneer of forensic science. In fact, Bell often used the word “elementary,” which means simple, when describing a successful diagnosis—something Sherlock Holmes became famous for saying.
Like Taylor, Bell, and other real forensic experts of that time, Holmes paid close and detailed attention to evidence at crime scenes. In Conan Doyle’s A Study in Scarlet, for instance, Holmes’s sidekick, Dr. Watson, says of Holmes: “His nimble fingers were flying here, there, and everywhere, feeling, pressing, unbuttoning, examining [everything at the crime scene].”2 Of course, today’s forensic scientists would never touch crime scene evidence with their bare hands, but at the time Conan Doyle was writing his stories, investigators were unaware of how important it was not to contaminate a crime scene with their own DNA and fingerprints.
Holmes’s meticulous forensic detective work captured the public imagination and remains popular even today, as TV shows such as Sherlock and Elementary make clear. In a way, all later CSIs and other forensic scientists followed in Holmes’s footsteps, combining scientific inquiry with deductive thinking. Because Conan Doyle did not know of the existence of DNA, Holmes never used DNA analysis to solve crimes. It was not until the 1950s, a little more than two decades after Conan Doyle’s death, that the existence of DNA was discovered, and it was not used in crime solving until the 1980s.
The use of DNA evidence in solving crimes came into the public consciousness in the 1990s as the result of a murder trial that became the center of public discussion: the Orenthal James, or O.J., Simpson trial in 1995. A former football star, Simpson was accused—and eventually found innocent—of murdering his ex-wife, Nicole Brown Simpson, and Ronald Goldman. Millions of people watched the prosecutors and defense attorneys argue the facts of the case, including DNA evidence. This trial was later dramatized in 2016 in the popular TV show American Crime Story: The People v. O.J. Simpson.
CSI, a TV show about forensic scientists in Las Vegas, Nevada, appeared in 2000, a few years after the O.J. Simpson trial. Its producers hoped to tap into the increasing public awareness of and interest in forensics and DNA. CSI was hugely successful, becoming the highest-rated show on television. It was so popular that it aired for 15 years, and 3 spin-offs were created: CSI: Miami, CSI: New York, and CSI: Cyber.
Today, largely as a result of these and other detective shows, public faith in the use of DNA evidence to solve crime has risen drastically. According to real CSIs, that confidence is sometimes a little misplaced. In truth, they point out, these shows sometimes glamorize forensics and exaggerate the capabilities and speed of DNA analysis and other forensic techniques. As one observer put it, this gives many viewers “impossibly high expectations of how easily and conclusively criminal cases can be solved using DNA analysis and other forensic science.”3
Nevertheless, DNA evidence can be a vital tool used by investigators to solve crimes that otherwise might not have been solved. Of equal importance is DNA evidence’s ability to clear innocent people who have been mistakenly convicted of crimes. DNA evidence can allow investigators to conclusively prove someone’s presence at a crime scene— or their absence. According to former Manhattan Assistant District Attorney Harlan Levy, DNA evidence “can avoid many miscarriages of justice that might occur without it, in a world where the truth is often hidden and elusive.”4
In order to understand how investigators use DNA as evidence, it is important to understand what DNA is. Essentially, DNA is the material that makes up genes. Genes determine the characteristics of a human, plant, or animal. In humans, genes determine things such as hair color, whether a person needs glasses, what kinds of diseases a person might be at risk for, and even certain parts of someone’s personality. Often, it is combinations of genes that make people who they are, and many of these are influenced by the way a person grows up. For example, a person with a particular combination of genes may be at risk for getting cancer, and a poor lifestyle may increase that risk—but there is no single cancer gene a doctor could flip on or off like a switch.
Every human’s DNA is made up of four compounds, which are called adenine, guanine, thymine, and cytosine. Adenine always pairs with thymine, and guanine always pairs with cytosine. However, the order in which these pairs appear in a person’s DNA is unique to everyone. Even identical twins may have small differences in their DNA. Figuring out in which order these pairs appear in a DNA molecule is called DNA sequencing, and this is how forensic scientists can tell who was at a crime scene.
Until the 1980s, police detectives investigating crimes were limited to collecting, examining, and interpreting a small range of evidence. They could collect and examine fingerprints, for instance—but not all criminals leave fingerprints, and it can be difficult to determine which fingerprints are related to the crime and which are not, especially if the crime occurred in a public place. Fingerprints can also easily smudge, making them unreadable, and they are far from permanent. In addition, only a small fraction of people have their fingerprints on record, so even when police are able to recover fingerprints from a crime scene, they sometimes have no way to make a match. This is why police will often ask suspects for their fingerprints—if they are a match to prints at the crime scene, investigators can reasonably argue that the suspect was present.
