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• 1.Crime Scene

  • The scene of a crime acts as a silent witness: the scene itself can tell investigators some facts that are easily ignored but crucial to solving the case.
    
    Dr. Edmond Locard, a French researcher known as the “Sherlock Holmes of France” came up with this basic principle of forensic science: Every contact leaves a trace. This became known as the Locard Exchange Principle. The principle states that “it is impossible for a criminal to act, especially considering the intensity of a crime, without leaving traces of his presence.” That means that a criminal is bound to leave evidence proving his identification, such as his hair, skin or even DNA. He may also leave behind any of his property that could help investigators to reconstruct the crime scene, such as his weapon or a piece of his clothing, or even drops of his blood from struggling with the victim.
    
    Therefore, the proper management and preservation of a crime scene are extremely important. Usually, the police are the first to arrive at a crime scene. After a detective determines that it could be a homicide, the police will preserve the scene for crime scene investigators. After the scene is made safe for investigators to work in, they will start to collect potential evidence. A crime scene investigator with a surgical mask will firstly track any direct evidence, such as a fingerprint or a blood drop left by the offender, and then collect anything else that may be used for further forensics. Photos of each corner of a scene are also taken. The front line management team is so important because even an accidental touch by an investigator may contaminate the evidence.

• 2.Even A Fly Can Tell

  • Can a little insect help to provide evidence? The answer is yes! The usage of insects in forensics is not rare. The first recorded case of using biology in crime investigation was contained in a handbook called The Washing Away of Wrongs, the world’s oldest book in forensic medicine produced by a Chinese official called Song Ci from the Southern Song Dynasty. He identified the murderer among several suspects by observing flies that had gathered on invisible blood residue left on a sickle owned by the murderer, and which was used as the murder weapon.
    
    Generally, investigators use forensics entomology to estimate the time of death. The accurate estimation of time of a victim’s death is important as it relates to a suspect’s alibi, which is a crucial element in proving a suspect’s guilt or innocence. Forensic pathologists are the first to try to estimate the time of death by examining a corpse. However, after around 48 hours of death, this method of estimation is less helpful. The eventual arrival of insects at the corpse can also reveal the time of death.  The rationale is simple: Insects regard the corpse as a huge feast, and different insects arrive at different times in a predictable order.
    
    Jean Pierre Megnin and Martin Hall were two key figures in the field of forensic entomology. They studied the insects that infest human remains. Megnin observed and recorded the predictable order in which different insects colonize after a corpse’s death and the different development stages of many species. Hall performed studies on blowflies, the insects with more than one thousand species in the world. Blowflies have an acute sense of smell and can detect the faintest smell of a decomposing body over a hundred meters away. They arrive at a corpse at different times depending on their different stages of development, and an entomologist can estimate the time of death by using this knowledge. 
    
    In 1935, a notorious case greatly increased the public trust in the application of forensic entomology. On one autumn day, 30 packages containing body parts were found. It was difficult to positively identify the victim because all the fingerprints had been removed.
    
    However, some maggots were feeding on the decomposing parts. The entomologists working on the case found that the maggots were a kind of blowfly. They estimated that the bodies had been dumped between 10 to 12 days ago, according to the feeding habit of such blowflies. That time frame coincided with the time of disappearance of two local women who had been missing. 
    
    The police were then able to link the two murders to Buck Ruxton, a highly respected doctor in the local community. One dead woman was Ruxton’s wife and the other was his maid. Later, the police were able to collect many more pieces of evidence to prove that Ruxton was the murderer. The use of forensic entomology was not the most crucial evidence used to prove Ruxton’s guilt, but it provided the initial valuable clue which gave the police a good starting point for furthering their investigation.
    
    While forensic entomology can give useful insights to detectives, it’s not as powerful and mysterious as some people think. Sometimes the public has misunderstandings about what it can do. In 1994, a BBC cartoon program called The Witness was a Fly exaggerated the role of forensic entomology and misled people. In the show, the maggot held up a placard that said “Murdered, 3 p.m. Friday.” In reality, insects cannot tell us the exact time when the victim was murdered, but can only give us an estimated time when they laid eggs on the body and an estimated time when the victim died. Moreover, in many cases, there are some variables, such as the weather and the insects’ habits that prevent entomologists from pinpointing a time of death.

• 3.Pathology and Anthropology

  • Sometimes a corpse can tell the truth. Pathologists are the people who try to find out the facts by performing autopsies or post-mortem examinations. An autopsy usually can reveal the cause of death. A pathologist checks any unusual elements found in or on a body. The elements and fragments that are found can help the police reconstruct the past.
    
    Our ancestors paved the way for modern forensic pathology. The first recorded forensic autopsy was in 44 BC. Julius Caesar’s doctor investigated the cause of the emperor’s death by using autopsy. Hundreds of years later, the Greek physician Galen produced his theories on human anatomy by dissecting monkeys and pigs. In the 16th century, Andreas Vesalius strengthened the science by comparing normal and abnormal anatomy.
    
    The work of pathologists is important because their examinations can provide detectives with an estimated time when death occurred. Pathologists reach their conclusion by applying multiple theories and methods. A pathologist will first measure the body’s temperature to estimate the time of death. A body loses heat at a constant rate of 1.8°F per hour until it reaches the ambient temperature. However, variables such as the weight, amount of fat, and size of the body can substantially affect the rate of heat loss.
    
    Pathologists also use the conditions of rigor mortis and putrefaction of a body to estimate the time of death, but neither is a perfect science as there could be natural variables and unnatural causes. Nowadays, modern technology has done pathologists a favor. For example, the Virtual Autopsy Table, a new medical visualization tool combining CT and MRI scans, transforms images of a body into a 3D model, helping pathologists save time and increase accuracy.
    
    Like pathologists, forensic anthropologists are specialists who analyze and get information directly from the dead body. The difference is that forensic anthropologists mainly study the bones and skeleton remains. Forensic anthropologists usually help to investigate and identify missing people.
    
    Between 1976 and 1983, a conflict called “Dirty War” broke out in Argentina. Civilians were kidnapped, tortured and killed by a military junta. Around 30,000 civilians became victims of the conflict and up to 10,000 people were “missing.” Then, a group of forensic anthropologists joined the investigation of the violence. That was the first time this method was used in a human rights investigation.
    
    These forensic anthropologists extracted DNA from the bones of those who were still unidentified and compared the results with those of living relatives. By 2000, they had identified 60 skeletons, though 300 more were still under investigation. Forensic anthropology is a new field which moves slowly but is making continual progress.

• 4.Fingerprinting, DNA and Facial Reconstruction

  • Remember Locard’s Exchange Principle? It states that “every contact leaves a trace.” Fingerprints are a form of direct evidence that help to bring criminals to justice. William Herschel was one of the first people to come up with the idea that fingerprints could be used to uniquely identify individuals. In the 19th century, Herschel was a magistrate in Hooghly, India.  He realized that fingerprints were unique and permanent and could be used to prevent fraud and impersonation. He set up a system for taking fingerprints of pensioners so that when they died, other people could not fraudulently get their pensions. He also began the fingerprinting of criminals who had received jail sentences so that impostors could not be hired to serve the sentences for them.
    
    By 1905, India, the United Kingdom, Hungary, Austria, Germany, Switzerland, Denmark, Spain, Argentina, the United States and Canada had each established their own fingerprints bureaus. Then the NYPD (or New York Police Department) brought fingerprints to other police departments in the US. Modern technology helped investigators to extract fingerprints from plastic bags  by using ultraviolet light and other methods to recover them.
    
    Although fingerprint analysis is an effective way to provide evidence, there are still many difficulties. For instance, it’s hard for investigators to examine the fingerprints when they have been lifted in a complicated context. Also, even a tiny contamination on fingerprints could lead to mistakes. Therefore, fingerprints are regarded as corroborative rather than sole evidence when presented in court.
    
    In the 1980s, genetic fingerprinting, now known as DNA profiling, was discovered. Traditional genetic fingerprinting heavily relied on bodily fluids and hair until 1999 when polymerase chain reaction (PCR) was used to develop a better method “low copy number (LCN) DNA profiling.” Investigators only need to get a few cells from a suspect to use this method. Then the British Forensic Science Service developed familial DNA searching. Today, in most countries, familial DNA searching for forensic purposes remains illegal to safeguard an individual’s civil rights. In the United States, it is only legal to use in California and Colorado.
    
    It’s a not an unfamiliar scene if you often watch crime dramas: Relatives are called by the police to see if they know the dead; it happens in the real world too. When investigators cannot identify a skull they found from a crime scene after using all available methods, they call forensic artists to reconstruct the faces. Strictly speaking,, facial reconstruction cannot be used as forensic evidence in a courtroom, but it helps the police to start the procedure of identification.
    
    The 22 bones of a human skull determine the shape of the face. The shape of these bones and the muscles attached to the bones explain the variation between individual to individual. Forensic artists need to look at the depth of the eye orbit and the shape of the brow to deduce the shape and prominence of a person’s eyes. They examine the size and position of the teeth to deduce the shape of the lips. It is hard to deduce the shape of the ear and nose because their cartilage decomposes after death.

• 5.Forensics in Digital Era

  • We live in a digital age with explosive information. Detectives rely on digital technology more than ever before. In forensic computing, data is recovered from computers for criminal investigations. Checking the browsing history, emails and online chatting history of a victim or potential suspect can provide the police more information about who the victim met with or what the suspect has done. This information gives vital clues to the police as to where to look next. By recovering the videos, images, and important information from the phone of a potential suspect, the police could find out what he has been doing and trying to hide. 
    
    Investigators can locate victims and suspects when a crime occurs by using digital technology. The GPS technology in smart phones makes it possible to pinpoint l on a map where the user has been. Even when the user turns off the location tracking function on the phone, investigators can still locate an approximate area from the network provider.
    
    However, each coin has two sides. The use of digital technology also brings with it inconveniences and limitations. More and more people upload their data and information to the cloud instead of storing them in their devices, which means it’s hard for the police to get all necessary data off the devices alone, and a suspect can change his information in the cloud remotely at any time. Ironically, older technology has turned out to be the best tool for criminals to avoid being tracked or investigated. A criminal may use a pay-as-you-go phone when committing a crime, and then eliminate all the evidence on the phone and dump it soon after the crime. He may also use an analog (rather than digital) camera, which does not embed metadata into the images captured.

• 6.The End

  • Besides the methods and tools mentioned above, other scientific disciplines and methods are also used during a forensic investigation. For example, toxicologists help the police to identify poisonous substances in the body and deduce how it was taken by analyzing what the toxin is, how much toxin was ingested, and where it was found in the body. Also, forensic psychology can be very useful during an investigation and even pivotal in reaching a verdict. If a person commits a crime when he is insane or under the influence of mind-altering drugs, the person will not be given punishment for the crime. Psychologists can also help the police to narrow down potential suspects by learning the suspect’s personality and behaviors which can be revealed from the crime scene.
    
    There is no single forensic method that can be solely used for investigating a crime and none of the forensic science is perfect; instead, using a combination of methods produces the most reliable evidence for solving the crime.
    
    All the evidence and reports obtained from forensics are scrutinized and finally presented to the courtroom. The courtroom is the important truth-finding place where the evidence is evaluated and weighed and a verdict is reached. As pointed out in the book, “without the scrutiny of the courtroom, the science assembled by forensic experts is meaningless.”

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