DNA identification provides a definitive method for establishing a person’s identity in forensic science, especially when visual or physical markers are lost. This process is regularly used to resolve missing persons cases, identify victims in mass fatality incidents, and provide evidence in criminal investigations. The time required to identify a body with DNA ranges from a matter of hours to many months. This variation depends primarily on the condition of the remains and the resources available for comparison.
The Essential Steps of Postmortem DNA Analysis
Generating a genetic profile begins with careful sample collection, targeting tissues most likely to have preserved DNA. For intact bodies, forensic scientists often collect samples of blood, muscle, or soft tissue. When remains are degraded or skeletonized, dense materials like bone and teeth are preferred, as their protective matrix shields the DNA from environmental damage.
After collection, the DNA must be isolated from cellular material through extraction and purification. The next step is quantification, which measures the precise amount and quality of human DNA present. A sufficient quantity of high-quality DNA is necessary for the next stage: amplification.
The Polymerase Chain Reaction (PCR) technique is used to amplify millions of copies of specific, short, repeating DNA segments known as Short Tandem Repeats (STRs). This amplification is targeted to the specific locations (loci) used in forensic databases. The resulting amplified fragments are then separated by size and detected using capillary electrophoresis. This process produces an electropherogram, which is a graphic representation of the DNA profile translated into numerical allele calls for comparison against reference samples or databases.
Typical Timelines for DNA Identification
The shortest identification times occur in highly controlled scenarios where reference samples and high-quality remains are readily available. When a fresh sample is collected and a known reference is immediately provided by a close relative, the entire process can be completed in 24 to 72 hours. This rapid turnaround is typically reserved for urgent cases and requires the laboratory to dedicate all available resources.
Standard forensic casework, involving non-severely degraded remains and a typical workload, takes longer. For most laboratories, generating a complete DNA profile from a recovered sample takes between one to three weeks. This range accounts for the sequential nature of the required laboratory steps.
Identification times extend significantly when the profile must be searched against large repositories like the Combined DNA Index System (CODIS). If the remains are from a historical case or a mass fatality incident, matching the profile can stretch into many months. This extended timeline reflects the necessity of coordinating with multiple agencies, the complexity of searching national databases, and the potential for a backlog of cases awaiting comparison.
Variables That Extend the Identification Process
Impact of Degradation
The condition of the remains represents the greatest variable affecting the DNA identification timeline. Environmental factors such as high heat, humidity, or prolonged exposure to water accelerate the postmortem processes that break down DNA molecules. While soft tissues quickly degrade, hard tissues like bone and teeth offer superior protection, preserving usable DNA for much longer periods.
Mitochondrial DNA Analysis
When a sample is severely degraded, standard nuclear DNA analysis (which examines DNA from the cell’s nucleus) may fail to produce a full profile. In these instances, scientists must use mitochondrial DNA (mtDNA) analysis, which is far more complex and time-consuming. Because mtDNA is present in thousands of copies per cell, it is more likely to survive degradation, but the analysis is labor-intensive and rigorous. An analyst may only complete three to four mtDNA cases per month, contrasting sharply with the potential for multiple nuclear DNA cases processed weekly.
Reference Sample Availability
The identification process is significantly delayed if a direct reference sample, such as a toothbrush or hairbrush from the deceased, is unavailable. In the absence of a direct reference, the profile must be compared against databases of known offenders or missing persons, or matched against the DNA of distant family members. Familial matching requires complex analysis of shared genetic markers to establish a relationship, a procedure that adds considerable time to the overall timeline.
The profile must also meet minimum quality standards, such as having a sufficient number of STR markers, to be accepted and searched in the national CODIS database. Meeting these standards can be challenging when dealing with highly degraded samples.