How Reliable Is DNA Evidence In Sexual Assault Cases?

The presence of DNA evidence in sexual assault, or lack of it, can greatly impact the outcome of a criminal or civil trial. However, despite what we see on television detective shows, DNA is not always considered conclusive proof of a rape or sexual assault. DNA testing also can be used to prove innocence and often is the key to winning a case and/or reducing a sentence.

The use of DNA in a trial can become complicated, and anyone who has been accused of rape or sexual assault may want to consult a sex crimes defense attorney who is highly experienced in this type of trial to ensure all opportunities are exploited to protect the person’s rights — and maybe even make the criminal charges go away.

In this article, we’ll examine the types of DNA evidence used in rape and sexual assault cases and how it’s used in defense.

What is DNA evidence?

DNA stands for deoxyribonucleic acid. Almost all living organisms contain DNA material. It is a self-replicating element of our body’s chromosomes and carries our unique genetic information. Every person in the world has different DNA, except identical twins.

There are two kinds of DNA. The first is found in bodily fluids, such as semen, saliva, and blood. The second type, epithelial DNA, comes from skin cells. DNA can be used to help identify and confirm the presence of a person in a specific location or interaction with another person.

DNA material is gathered at the scene of a crime where bodily fluids are present. It is also gathered on the body and clothing of the victim. To rule out the presence of other people besides the victim and perpetrator of a crime – people who may inadvertently leave DNA at the scene – law enforcement personnel will take DNA samples from officers, friends and family, witnesses, and others the victim may have had sex with within 24 hours of the crime.

DNA material is acquired from the body of a victim by medical personnel soon after a crime happens. Special nurses are trained to complete “rape kits”, which use medical tools to easily and cleanly gather DNA samples. These nurses are called Sexual Assault Nurse Examiners (SANE). It’s important for the evidence not to be disturbed until the victim can be examined, so victims often are advised not to use the bathroom, bathe, change clothes or clean their fingernails until they visit a SANE.

For DNA to be accepted as authoritative evidence in a sex crimes trial, it must be gathered properly by trained investigators, and the gathered evidence must follow a proper chain of custody to maintain its integrity.

How is DNA used as evidence in a sexual assault trial?

Forensic scientists can analyze DNA and use the profile to match perpetrator records in the FBI’s Combined DNA Index System (CODIS). This is useful when the identity of a rapist is unknown. DNA analysis also is convenient for matching DNA with a specific person who has been accused. If the person is not listed in the CODIS, the court can order a DNA sample to be taken. The CODIS has formally existed only since 1994.

In general, prosecuting attorneys must prove two facts to successfully convict someone of rape or sexual assault: 1) there was sex between the accused and the accuser; and 2) it was not consensual sex. DNA can only be used to help prove the first of the two facts, but it also can be used to rule out the presence of an accused person or at least create the benefit of doubt.

In most cases, any existing DNA evidence is primarily used by prosecuting attorneys to build a case against the accused. The hard-scientific evidence provided by DNA can help verify facts that can only be implied by witness interviews and other “soft” evidence. However, in many sexual assault court cases, the evidence presented is not conclusive or leaves room for interpretation.

Because of the limitations of using DNA as evidence, DNA findings are often combined with other evidence to gain a conviction. In some cases, the evidence appears to be obvious, as in the 2017 use of DNA in a rape case in Omaha, Nebraska, to identify a serial rapist who had broken into random homes and raped four women at knifepoint. Other evidence sometimes used in concert with DNA evidence includes evidence of injuries consistent with rape or sexual assault, phone records, text messages, social media posts and interviews with potential witnesses.

If it is determined there is no DNA matching the accused, it causes doubt as to whether the rape took place.

The Problem with DNA

Sometimes DNA evidence isn’t usable or can be proven corrupt if the samples of bodily fluids haven’t been collected or transferred properly. There are cases where DNA evidence has been falsified by law enforcement officers to ensure a conviction.

Even if the integrity of samples can be confirmed, DNA evidence can prove only certain things. If DNA belonging to the accused person is found at the scene of the crime or on the body of the victim, it proves they did spend time together. It may even prove they had sex, but the DNA itself cannot prove the sex was not consensual. It also doesn’t rule out other possibilities. For example, a victim also may have had sex with someone else who could be the person who committed the assault.

If DNA of the accused is NOT present, it doesn’t necessarily mean a rape or sexual assault didn’t take place, so prosecutors must look for other ways to prove a rape took place. Injuries consistent with sexual assault, for example, might get a jury to consider the possibility that the alleged sexual assault did take place even if DNA isn’t available—especially if there are coordinating injuries on the bodies of both the victim and the accused. However, injuries are not always present, even if a rape did take place.

It’s important for a defense attorney to thoroughly explain applicable limitations of DNA analysis to a jury. People who serve as jurors are regular citizens who hear about sexual assault through friends and in the news or watch fictionalizations of rape and sexual assault cases on television. It’s common for jurors on sexual assault cases to put too much trust in DNA evidence because they are used to seeing it on TV. This is sometimes called the CSI effect. It’s the defense attorney’s job to keep jurors from drawing the wrong conclusions and making unfounded assumptions that the accused person did in fact commit the crime.

In addition to these problems with DNA evidence, when a city, state or the federal government prosecutes a sexual assault case, their efforts are narrowly focused on proving that a sex crime DID occur, so analysis can be slanted toward prosecution. The evidence is not always helpful in defending someone who has been falsely accused (i.e., proving a crime did NOT happen). Defense attorneys must find other means of defending the rights of the accused.

How DNA is Used to Defend Against Rape or Sexual Assault Charges

If an accused person’s DNA is not found at the scene of a crime or on the body of the victim, a defense attorney may successfully convince the court to drop the charges, because this suggests the person could not have been at the scene of the crime, if there is no other reason the DNA evidence might not be present. This is the simplest use of DNA in rape and sexual assault defenses.

Defense becomes more complex when the accused was at the scene of a crime but did not commit the crime. Because rape and sexual assault often involve interaction between people who know each other, it’s not unusual to find DNA for the accused at the scene of a crime or on the body of the victim. It’s the prosecution’s job to prove the crime beyond the person’s presence on the scene. Defense is often a matter of getting the court to focus more on the question of whether sex was consensual than on proving the accused was present.

A famous case in which charges were dropped due to the doubt created by DNA evidence involved basketball star Kobe Bryant. In this case, DNA of other people the victim had sex with was gathered at the scene and on the victim’s body. This information was used, in addition to evidence surrounding her injuries, to cast doubt on the claim that sex with Mr. Bryant was not consensual.

No matter what the situation, if you or someone you know has been accused of rape or sexual assault, you may want to contact an experienced sex crimes attorney as soon as possible. As early in the process as an investigative interview, it can be easy to inadvertently provide evidence that can be used against you. Your attorney can help you navigate the challenges of a successful defense.

If you or someone you know has been accused of sexual assault or sexual harassment, call the Berry Law and make an appointment for an experienced sex crimes attorney to hear your story.

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