In forensic serology, saliva is a crucial biological fluid analyzed to identify individuals, link suspects to crime scenes, and gather other significant investigative information.
Saliva is an exocrine secretion produced by salivary glands in the mouth. It primarily consists of water, but also contains electrolytes, mucus, antibacterial compounds, various enzymes (like amylase), and epithelial cells. These epithelial cells are particularly valuable in forensic science because they contain nuclear DNA.
Role of Saliva in Forensic Investigations
The presence of saliva at a crime scene, on an object, or on a person can provide key evidence. Forensic serologists examine suspected stains to determine if they are saliva and then perform further tests.
- Identification: The cellular content of saliva contains DNA, which can be extracted and profiled. This DNA profile can then be compared to reference samples from suspects or databases (like CODIS) to establish identity or linkage.
- Source Material: Identifying a stain as saliva indicates the source was the mouth, narrowing down possibilities in an investigation.
- Contextual Evidence: Where saliva is found (e.g., on a cigarette butt, an envelope, a drinking container, clothing) provides context about how an individual might have interacted with the scene or object.
Applications of Saliva Analysis
Based on serological testing and analysis of its cellular content, saliva has proven to be of wide use in crime detection, drug and alcohol abuse, hormone identification, cases of poisoning and animal bites.
Here are some specific examples of its forensic applications:
- Crime Detection: Identifying suspects from discarded items containing saliva (e.g., chewing gum, cigarette butts, bottle necks) or from contact trace DNA left during a physical altercation.
- Drug and Alcohol Abuse: While blood and urine are more common, traces of drugs or alcohol might sometimes be detectable in saliva, providing supplementary evidence.
- Hormone Identification: Hormones present in saliva can potentially provide information about the physiological state of the individual.
- Cases of Poisoning: Detecting ingested poisons or toxins that might be present in residual saliva samples.
- Animal Bites: Analyzing saliva left in bite marks can help identify the animal involved, which might be relevant in cases involving animal attacks or zoonotic diseases.
Methods of Analysis
Forensic serologists use several methods to detect and analyze saliva:
- Presumptive Tests: These indicate the possible presence of saliva. A common test looks for the enzyme amylase, which is abundant in human saliva.
- Confirmatory Tests: These tests are more specific and confirm the presence of saliva. Techniques like immunochromatographic strip tests targeting specific salivary proteins can be used.
- DNA Analysis: Once a stain is identified as saliva, DNA extraction and profiling are performed if sufficient cellular material is present.
Comparison Table: Saliva vs. Other Fluids in Forensics
| Fluid | Primary Forensic Value | Common Analysis | Key Use Cases |
|---|---|---|---|
| Saliva | DNA, source identification (mouth) | Amylase test, DNA analysis | Discarded items, bite marks, sexual assault (sometimes) |
| Blood | DNA, bloodstain pattern analysis, toxicology | Presumptive/confirmatory tests, DNA, toxicology | Violent crimes, accidents, poisoning |
| Semen | DNA, presence of spermatozoa | Acid phosphatase test, PSA test, DNA analysis | Sexual assault cases |
| Urine | Toxicology (drugs, alcohol), sometimes DNA | Chemical tests, toxicology, DNA (limited) | Drug/alcohol testing, some sexual assault cases |
In summary, saliva is a valuable forensic sample because it is frequently encountered at crime scenes and is a rich source of DNA, enabling various types of analysis crucial for linking individuals to criminal activities and providing contextual information.
