Forensic biologists examining evidence using an alternate light source

The Forensic Biology section of the Forensic Science Laboratory performs serological and DNA analyses of physiological fluids and other biological materials from the human body for identification and comparison purposes. The type of material typically examined includes, but is not limited to: blood, semen, saliva, urine, skin cells, and hair collected at crime scenes and from articles of physical evidence. These types of biological materials are frequently deposited or exchanged during the commission of violent crimes such as homicides, rapes, assaults, burglaries, and hit-and-run fatalities. The Lab’s analysis of biological crime scene evidence may link that material to victims and/or suspects, thus aiding criminal investigations.

The Forensic Biology section analyzes cases submitted from over 50 different law enforcement agencies throughout Westchester County. Personnel from this section perform laboratory analyses on samples submitted by police agencies and the County District Attorney’s Office. They also assist in the processing of crime scenes.

Biological Evidence
Upon submission, articles of biological evidence are stored in a secure refrigerated walk-in cold room pending analysis. An analyst is assigned to a specific case and will bring the evidence to an evidence examination room, where it is documented and analyzed. The alternate light source (ALS) can be utilized to locate stains that may contain blood, semen, saliva, or urine. These stains will undergo a series of presumptive screening tests. Any stains testing positive during this stage may then be subjected to more extensive testing, including DNA analysis. The DNA profiles generated from these stains can then be compared to samples taken from known sources (victims, suspects, etc.).
Some biological materials containing DNA may not be suitable for presumptive screening, such as skin cells and hair. These types of material are collected and preserved in the laboratory for possible future DNA analysis.

The Forensic Biology section performs DNA STR (Short Tandem Repeat) analysis. STRs offer the advantages of short analysis time, a high degree of discrimination, and the ability to look at small and degraded samples of DNA. For example, the tissue adhering to the end of a pulled head hair, or skin cells from under the nails of a victim can be compared to possible contributors.

This laboratory currently utilizes high-throughput Applied Biosystems 3500 Genetic Analyzers for DNA analysis. In addition to the analysis of autosomal STR’s, the laboratory performs STR analysis of the Y chromosome, found only in males. Analysis of Y STRs is helpful in the investigation of sexual assault cases involving multiple male assailants and in highly degraded samples.

The Forensic Biology section is linked to the FBI CODIS (Combined DNA Index System) DNA database network comprised of local, state, and national databases. The Forensic Biology section houses the local crime scene sample database for Westchester County. Through this network, the Laboratory can take an unknown crime scene DNA profile and compare it to other unsolved cases throughout the county, state, and country. The same crime scene sample will also be compared against convicted offender databases. Links made using CODIS allows investigators from different jurisdictions working on serial-type cases to share important investigative information at an early stage. CODIS also maintains a dedicated database for unidentified human remains.

Field Sampling
In addition to providing state-of-the-art DNA technologies, the Forensic Biology section, upon request by a police agency, will assist in the detection and collection of biological evidence at a crime scene. The laboratory can dispatch personnel trained in the use of alternate light sources and chemical enhancement techniques for the detection of blood and other biological materials that may contain DNA.

Please note that, as of December 17, 2020, the Forensic Laboratory no longer provides services in bloodstain pattern (“blood spatter”) analysis.