By John Brennan
Updated Aug 30, 2022
stevanovicigor/iStock/GettyImages
Over the past two decades, DNA profiling has become an indispensable tool in forensic science. By comparing highly variable genomic regions from a sample with those found at a crime scene, investigators can establish guilt or innocence with remarkable precision.
DNA profiling’s primary strength lies in its specificity. Even trace amounts of genetic material can yield enough data for analysis. Forensic laboratories typically examine at least 13 short tandem repeat (STR) markers. With 13 markers, the likelihood that two unrelated individuals share an identical profile is estimated to be less than 1 in 10 billion, making DNA an exceptionally reliable match tool when samples are collected and processed correctly.
While DNA evidence is powerful, it should be considered alongside other evidence types. The “CSI effect” has heightened public expectations, sometimes leading jurors to overvalue DNA findings. Additionally, maintaining expansive DNA databases raises ethical concerns, especially when samples are stored from individuals who have never faced criminal charges. Large‑scale collection operations, or “DNA dragnets,” further spark debate over privacy and due process.
Like any forensic technique, DNA analysis is vulnerable to human error. Contamination during collection or laboratory work can compromise accuracy. Generally, DNA evidence is more useful for excluding suspects than definitively proving guilt. The Innocence Project at the New York Benjamin N. Cardozo School of Law has leveraged DNA profiling, among other evidence, to exonerate more than 100 wrongfully convicted inmates.
