Until DNA evidence was introduced, the only physical evidence to identify a suspect was fingerprints. Fingerprint evidence has always been reliable, but since DNA has been introduce it has become the evidence of choice when playing a criminal suspect at the crime scene. Everybody has a unique set of DNA, except for identical twins. By using scientific tests, crime scene analysts are able to compare two samples of DNA. These usually come from small fragments of the culprit which were left at the crime scene such as hair, blood or saliva. Usually when these tests are done, if the samples match, it is very likely that the suspect was at the scene of the crime.
The science behind DNA is complicated, and not many lay people understand it. However, it is becoming more and more commonly used by crime labs and law enforcement agencies. Once DNA is found from a suspect at the scene of the crime, police automatically assume that person is the culprit. DNA evidence is based on the fact that it is highly likely that anyone with matching DNA at the crime scene will be involved in the crime, however expert criminal attorneys can sometimes throw into question even the most incriminating samples of DNA. This happened in the famous OJ Simpson murder trial, where the criminal defense made the jury question a mountain of DNA evidence.
DNA evidence is also used to exonerate past crimes. Sometimes old evidence from a crime scene, such as blood or semen still remains. If that DNA is tested and does not match with the person who was convicted of that crime, then it would provide reasonable doubt because another person must have been there. Since the introduction of DNA technology, many appeals have been made on this basis.
One of the best functions of DNA is that it can eliminate people as suspects of a crime. Because it is so accurate, the culprits hair, blood, semen or saliva can be compared to any criminal suspects that the police have in custody. If the sample does not match the suspect, then they will likely be removed from suspicion. Fingerprints work in the same way, however they are not always left at every crime scene, depending on the nature of the crime. DNA is almost always left somewhere. The police can also use the victim’s DNA in some types of cases, such as murder or assault, if it is found on the suspect’s clothing, in their home or in their vehicle.
Using DNA in Appeals
Sometimes an innocent person can be wrongly imprisoned for years or even decades on serious charges such as rape, murder or robbery. Usually, these people were convicted based on the testimony of others and no physical evidence was found or understood at the time that they were on trial. However, the introduction of DNA allows us to re-examine evidence that was previously misunderstood in order to exonerate these innocent people of their crimes.
Often there is a sample of DNA that was at the crime scene that is compared to the innocent person’s DNA. If this was a key piece of evidence during the trial, it might make a strong basis for a criminal appeal. Sometimes DNA evidence can outright prove that the wrongfully convicted person did not commit the crime. Also, the DNA of the real culprit might be on file in a police database. In many instances of serious criminal offense, the real criminal will be found and put on trial.