Forensic Science and DNA in Crime Solving

Forensic Science is defined as the "application of science to law and the investigation of criminal activity" (Forensic Files). Forensic science is made up of many different areas of expertise that are interrelated and work together to solve even the most baffling of crimes. Forensic scientists are now able to turn even microscopic evidence into strong physical evidence. This allows investigators to solve crimes that were once impossible to solve. That includes crimes with no witnesses, no suspects, no known motives, no visible evidence, and in some cases-no bodies. With the advances of forensic science and DNA testing, comes a stronger understanding and acceptance of its validity by society. Jurors were not so sure about DNA evidence when it was first used in courtrooms, since their knowledge of the subject was limited. Now, it is very seldom that a prosecutor will rely solely on circumstantial evidence when trying a criminal case.

There are many uses for DNA and it has quickly become one of the most widely used forensics tools for investigators. DNA can positively identify human remains, eliminate or exclude a person as a suspect, exonerate innocent people, prove a suspect's involvement in a crime, and place a suspect at the scene of a crime. In cases that involve blood evidence but missing a body, reverse paternity DNA testing can be done to determine if the blood found belongs to a particular person.

It was in 1984 that Sir Alec Jeffreys developed the first DNA profiling test. DNA (which stands for deoxyribonucleic acid) "is the genetic material found in the body's nucleic cells (those with a nucleus) such as white blood cells, semen, bone, skin, and hair"(Wells). Aside from the usual blood and semen that can be found at a crime scene and tested, DNA can be found on items that most criminals would never even think of. Cigarette butts, cups, beer bottles, envelopes, lipsticks or chap sticks, and even tissues can be used to obtain a DNA sample.

DNA profiling was first introduced to US criminal court during a rape case in Florida in 1987. Tommy Lee Andrews, a factory worker, was convicted of a series of rapes based on DNA evidence (Wells). In 1989, the first post conviction DNA testing resulted in the exoneration of an innocent man convicted of murder in Virginia. David Vasquez, a borderline retarded man, allegedly confessed and pled guilty to sexually assaulting and murdering a woman in 1984. He later said he had only "dreamed it." DNA testing later proved that the true killer was Timothy Spencer, a man who was responsible for several other rape-murders. With this DNA test proving his innocence; Vasquez was released in 1989 after serving five years. Although he was not tried for the Vasquez case, Timothy Spencer was convicted of two other rape-murders. He became the first person in the United States to be executed based on DNA testing (Connors).

In 1992, the FBI started a national DNA database. The goal was to get each state to build its own DNA database by obtaining DNA samples from all convicted offenders, feeding them into a database, and linking them together so that DNA found at crime scenes could be matched to known offenders (Willing). Every state now has a database, and all offenders convicted of violent and/or sexual crimes are required to submit to a DNA sample recovery. This allows investigators to obtain a DNA sample from a crime scene and feed it into the database to determine if it matches any known offenders.

Along with human DNA evidence, DNA markers are also found in plants and animals. When Shirley Duguay was reported missing, police found her car abandoned in a field with blood spattered on the windows. Police searched the area and found a bag that contained a bloody jacket and a pair of men's shoes. On the jacket, police found white cat hairs. Forensic tests proved that the cat hairs came from the suspect's cat, Snowball. It was the first time animal DNA testing had ever been done and the first time it was ever used to convict someone of a crime (HBO Autopsy 4)

In a murder case in Arizona, seed pods from a tree were found in the suspect's truck. The seed pods looked similar to ones that grew on a tree in a remote wooded area. The murdered woman's body was found lying beneath this particular tree. A molecular geneticist was able to prove through non-human DNA testing that the pods found in the truck came from the same tree. That proved that the suspect's truck had been at the crime scene and had brushed against the branch of the tree, causing the pods to fall into the bed of his truck. This breakthrough resulted in the first conviction based on plant DNA (Forensic Files).

Even bodies of water have their own "fingerprints." Two boys were attacked while fishing in a pond. Three local teenage thugs had been seen in the area around the time of the attacks. When questioned, the three teenage suspects denied any involvement and claimed they had never been at the pond. Police found a pair of muddy sneakers in the home of one of the suspects. The boy claimed he had gotten mud on his shoes by jumping in mud puddles. Skeptical, police took the shoes to be tested. Scientists located a number of diatoms, microscopic creatures that live in water, on the shoes. There are many species of diatoms, but not all species live in all bodies of water. That means that there are distinguishable combinations of different species in different concentrations that are unique to each body of water. In comparing the diatoms on the shoes with a sample of water from the pond, scientists were able to conclude that the mud on the shoes could not have come from any other source. This resulted in convictions for all three suspects (Forensic Files).

There are other important areas of forensic science that are just as valuable as DNA, and sometimes the only hope investigators have of solving crimes. Trace evidence analysis is one of these areas. Trace evidence analysis uses trace evidence, usually hair and fibers, to tell a story about what occurred at a crime scene. Trace evidence is "material deposited at a crime scene that can only be detected through a deliberate processing procedure. Any individual entering any environment will deposit traces of his or her presence, and this material can be used as evidence" (Court TV). Fiber and hair comparison analysis is the process that identifies the source of hair and fibers found on a victim or at the crime scene. Carpet fibers, dog hairs, human hairs, paint particles, glass particles, dirt, and even chewed gum are always looked at as possible clues and are collected for analysis.

Hair analysis can tell examiners if the hair came from a human or an animal. When experts examine a human hair, they can identify what area of the body it came from and the race of the person it came from. Experts can also identify characteristics that indicate if the hair has been cut, colored, permed, bleached, burned, or crushed. The root is examined to determine if the hair fell out or if it was forcibly removed. If only a few hairs were found at a crime scene, investigators can start by learning if the source of the hairs was the victim, or if they are foreign hairs. If they are pubic hairs, police can assume a sexual assault took place, especially if they were forcibly removed. And at least they would know the race of the suspect that they are looking for. If a suspect is found, then the hair can be used as a source of DNA to compare to the suspect's DNA.

Blood spatter analysis and crime scene reconstruction are other areas of forensic science that are highly valuable in piecing together evidence to determine how an assault occurred. In cases of suicide, investigators have an added burden of trying to prove whether or not the deceased took his/her own life. Blood spatter analysis tells police where the assailant and the victim were positioned, at what angle the blows or gunshots were delivered and the relative force used in the attack. The location and direction of blood spatter can help to prove or disprove any claims that a suicide took place. In many cases in which the cause of death is a gunshot wound, this is easier to prove. Crime scene reconstruction involves piecing together all of the evidence to determine the sequence of events-the nature of the attack, the location of the attack, the position of victim and offender, the time of occurrence, and type of weapon used.

Gunshot residue analysis studies the patterns and locations of gunshot residue that is always present after a gun is fired. The person holding the gun will get gunpowder on his/her hands. Blowback usually causes gunpowder residue to land on the clothing of the person shooting the gun. In one case, a woman claimed that she was asleep in a separate room when her husband was shot and killed by an intruder. When police found her nightgown by the bed that her husband was killed in, she said she left it there earlier in the evening after having sex with him. The nightgown tested positive for gunpowder residue. The reason that is significant is because of the location of the gunpowder residue on the gown. It was all on the front. That told investigators that she was wearing that nightgown when she pulled the trigger (Forensic Files).

Ballistics is another area of forensics that is dedicated to the study of guns. Ballistics experts can determine how close a gun was to the body when it was fired, if the person was shot from the front or back, and the path that the bullet traveled from the time it was fired until the time it became embedded in a person or object. This "mapping" process can pinpoint the exact location and position the victim was in when shot. Experts can also determine if a bullet (retrieved from a shooting victim) matches a suspect's gun.