Who doesn't love a good crime show? The modern Sherlock Holmes uses the amazing advances in forensics and technology to track down the most unlikely suspects and convict them without questioning the validity of the evidence. In many cases, the deciding factor in these fictional dramas is DNA evidence.
While the use of DNA as a crime fighting tool has certainly revolutionized investigative police work, its portrayal on television as irrefutable proof of someone's guilt has potentially tainted the opinions of juries. In truth, the analysis of DNA evidence may not be so trustworthy.
When evidence is not proof
The discovery that each person carries a unique sequence of DNA revolutionized criminal investigations, allowing law enforcement to focus on a particular suspect more quickly. However, finding DNA at the scene of a crime is not as neat and easy as TV detectives make it seem. Some important elements of criminal investigation include the following:
- Forensic technology needs only a few cells to detect DNA.
- Skin cells, hair and saliva contain DNA.
- People leave trace amounts of DNA wherever they go.
- You transfer your DNA to others when you come in contact with them.
If you were at the crime scene at any time, it is likely that you left traces of your DNA behind. Even more compelling, you may never have been at the crime scene, but you possibly transferred your DNA to someone else who then carried it to the crime scene. A stray hair or dead skin cells on someone's clothing may have dropped into the crime scene, and investigators gathered it as evidence.
Researchers have conducted experiments demonstrating how secondary DNA can appear on a weapon 85 percent of the time following a handshake, and in some cases, there is more secondary DNA than DNA evidence from the person who actually held the weapon. If you had physical contact with the person who used a weapon to commit a crime, trace amounts of your DNA could be on the weapon.
Limitations of DNA phenotyping
While crime shows fictionalize the capabilities of investigators using DNA, phenotyping — the use of DNA to reconstruct facial features — is much more limited than portrayed on TV. Phenotyping cannot predict many external characteristics, such as face shape or nose size, but it can tell investigators the color of the skin and hair as well as the sex of the person who left the DNA behind. Investigators can use phenotyping to narrow a pool of suspects. They can also use this technology to help exonerate those whom a jury has wrongly convicted.
If Tennessee detectives found your DNA at the scene of a crime, that doesn't mean your fate is sealed. While DNA is a powerful investigative tool, it has its flaws and limitations, which a skilled criminal defense attorney can exploit.