What Is DNA Evidence and How Is It Tested?
What Is DNA?
DNA (or deoxyribonucleic acid) is a strand of genetic material that is found in human blood, saliva, hair skin or semen. DNA has been called the “blueprint of life” since it contains the instruction manual necessary to make an organism grow and develop. The majority of the DNA is identical from one human to another, but there are locations in the DNA that have been found to differ from one individual to another, with the exception of identical twins. The regions of DNA that differ from one person to the next are compared in DNA identification testing.
DNA is found in all cells with a nucleus and is the same throughout the body, so virtually every fluid or tissue from a human contains some DNA and can be analyzed by DNA identification testing. DNA also is stable and does not vary over time, so samples collected years ago may be compared to samples collected recently.
How Is DNA Tested?
When DNA testing is done, several basic steps are performed regardless of the type of test. The general procedure includes:
- The isolation of DNA strands from an evidence sample containing DNA of unknown origin and, generally at a later time, the isolation of DNA from a known sample (for example, blood from a suspect) for comparison
- Once isolated, the DNA sample is processed (as described in step 4) so that test results may be obtained
- The determination of the DNA test results (or types) from specific regions of the DNA
- The usual means of DNA analysis is done by the polymerase chain reaction (PCR) method, a kind of molecular copying technique that can generate reliable data from minute amounts of DNA in crime scene samples. In the not-so-distant future, PCR-based test using mitochondrial DNA will successfully obtain results from a shaft of hair or dried bones.
- DNA databases are used to compare DNA patterns in the sample to those of the population at large so as to provide a statistical likelihood in the comparison.
Each comparison (from different sites on the genetic material and/or from different samples) provide an opportunity for an “exclusion” if the known individual being used for comparison is not the source of the DNA from an evidence sample of unknown origin. If, however, the known individual is the source of the DNA on the evidence sample, additional testing will continue only to include that individual as a possible source of the DNA. This method operates to increase certainty in the DNA testing world.
How Does DNA Get to a Crime Scene?
There is known DNA evidence (produced by the victim) and there is evidence produced by a suspect (foreign depositor). This evidence must be collected by a definite protocol because deviation from this collection method might spark a courtroom challenge to the reliability of that evidence.
How Is a Private Investigator Used in a Case Where DNA Evidence Is Employed?
A private investigator may be retained and used to challenge the manner in which DNA evidence was gathered and handled by their opponent. The private investigator might look for evidence to substantiate a challenge to laboratory staff’s credentials or he might look for evidence that their test results have been successfully challenged in other cases.
When Is DNA Evidence Used?
DNA evidence is used in criminal prosecutions (to show a suspect is the perpetrator of a crime) and in an increasing variety of civil cases (to prove that an individual was wrongfully convicted and imprisoned for a crime, to show paternity and to establish lineage in estate matters.)
As an example, “wrongful conviction” cases have created a new type of litigation. Civil lawsuits are routinely brought by those exonerated through DNA evidence against police, prosecutors and the forensic laboratories who helped bring about the wrongful conviction. For example three young men who played on Duke’s Lacrosse team and were falsely accused of rape and wrongfully prosecuted for that crime over a twelve-month period sued a North Carolina District Attorney and thirteen others. The trio also sued the laboratory used by the prosecutors for withholding evidence that pointed to their innocence. This is the laboratory that initially attested to a match between their DNA and samples taken from their accuser. This laboratory is now under scrutiny for its handling of evidence in this and other cases. Your fictional PI (who could easily have a scientific background) might be involved in gathering evidence about how certain laboratories are crooked, how they employ “bad science,” or even what makes some scientists charlatans.
(Excerpt from How to Write a Dick: A Guide for Writing Fictional Sleuths from a Couple of Real-Life Sleuths by Shaun Kaufman and Colleen Collins)
Shaun Kaufman is a Denver, Colorado defense lawyer who has spent nearly three decades sharpening his instincts and winning cases in courthouses. He has tried cases ranging from jaywalking to first-degree murder.
To contact Shaun Kaufman Law call 303-309-0430, or fill out the form on the right side of this page and Shaun will get back to you as soon as possible.
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