Forensic serology is a specialized field within forensic science focused on examining bodily fluids discovered at crime scenes. This discipline involves the detection, identification, and classification of these biological materials. It provides initial insights into evidence, helping to piece together events and link individuals to a crime.
Types of Biological Evidence
Forensic serologists frequently encounter and analyze various biological fluids. Blood is a common type of evidence, significant for its potential to provide DNA and to indicate the presence of injury or struggle. Semen is another type of biological evidence often found in sexual assault cases, and its presence can be crucial for linking a suspect to the incident. Saliva is also a source of biological evidence, found on items like cigarette butts, envelopes, or bite marks, and it can yield DNA for identification. Other bodily fluids, such as urine, vaginal secretions, sweat, and tears, can also be collected and examined.
Preliminary Testing Methods
Initial screening for biological fluids at a crime scene often involves presumptive tests, offering a rapid indication of a fluid’s possible presence due to their high sensitivity. For instance, the Kastle-Meyer test is commonly used to screen for blood, relying on hemoglobin’s activity to turn a colorless solution pink upon reaction with a reagent and hydrogen peroxide. Similarly, the acid phosphatase (AP) test is a preliminary method for detecting semen, identifying the enzyme abundant in seminal fluid by producing a characteristic purple color. While these tests are valuable for quick assessment and can detect minute traces of a substance, they are not definitive; false positive results can occur with certain environmental factors or other substances. Species identification tests, like the precipitin test, may also be used in initial stages to determine if a suspected bloodstain is of human or animal origin.
Detailed Examination and Analysis
Following preliminary tests, forensic serology uses confirmatory tests for definitive identification of biological fluids. For blood, tests like Takayama or Teichmann involve adding specific chemicals to form characteristic hemoglobin crystals, observed microscopically. For semen, analysis includes microscopic identification of spermatozoa or immunochromatographic tests for prostate-specific antigen (PSA or p30). The p30 test indicates the presence of a specific antigen found in semen, similar to a pregnancy test. Traditional blood grouping systems like ABO have largely been supplemented by DNA analysis; serology now serves as a precursor to DNA profiling, identifying fluid types and preparing material for DNA extraction and analysis to identify the biological material’s source.
Serology’s Role in Investigations
Forensic serology findings provide foundational evidence guiding investigations. Identifying fluid types narrows possibilities; blood indicates violence, semen suggests sexual activity. Combined with DNA profiling, serological analysis links individuals to crime scenes or victims. This evidence can corroborate or refute statements, strengthening or weakening a case. DNA profiles from biological evidence can be uploaded to databases, potentially identifying perpetrators, and this objective evidence contributes to understanding criminal incidents.