DNA stands for deoxyribonucleic acid, a substance present in your genes and those of all other human beings. Your DNA profile identifies you in much the same way as your fingerprints do. However, as FindLaw explains, forensic experts need only an incredibly small sample of your DNA to identify it as yours.
Often called trace DNA or touch DNA, these are the extremely tiny amounts of yourself that you leave everywhere you go on everything you come into contact with.
Sources of DNA evidence
Trace DNA evidence can come from a variety of sources, including the following:
- Your saliva
- Your sweat
- Your blood
- Your urine
- Your skin cells that you constantly shed
Most forensic investigators conduct an initial polymerase chain reaction test on each DNA sample they work with. Once they complete this PCR test, they then compare its results with a DNA sample you provide. Alternatively, they cross-reference the results with the thousands of DNA profiles contained in government databases.
Either way, the comparison can either identify you or rule you out as the person who left the tested DNA sample.
Most experts claim that a DNA match carries a 99% certainty. However, if you face criminal charges where DNA evidence could convict you, your attorneys may well want to retest the DNA sample the forensic lab used in a lab of their own choosing. Why? Because DNA results are not foolproof.
Most state-run DNA labs have backlogs of samples waiting to be tested. Sample mix-ups are not at all uncommon. In addition, lab workers can contaminate samples through sloppy, inadequate or inappropriate testing procedures.