Forensic Biology (DNA)

Scientists in the Forensic Biology Unit routinely examine evidence for the presence of biological material and its suitability for the DNA analysis process. 

Biological Screening

Some cases start with a screening process to determine if probative biological fluids may be present on an item of evidence by utilizing several presumptive and confirmatory tests.  Screening is used primarily on sexual assault and homicide evidence to deduce if any stains or samples may have forensic significance to the case at hand.

The Forensic DNA Process

After the screening process, or for casework in which biological fluids may not be present (e.g., items that have only been touched or handled by a suspect), the evidence can move forward for DNA analysis.  In general, the DNA analysis process follows five steps:

1. Digestion and Extraction: A portion of evidence is placed in a tube, and the addition of a series of chemicals allows the DNA to be released from the cells and purified.
2. Quantification: The sample is run on an instrument to determine how much DNA starting material is present. This is a necessary step for downstream processing.
3. Amplification: Using polymerase chain reaction (PCR) technology, fragments of the DNA sample called short tandem repeats (STRs) are copied millions of times in order to be analyzed by the capillary electrophoresis instrument in the next step.
4. Capillary electrophoresis: An electrical current is applied to the DNA fragments from each sample to allow separation by size as the fragments pass a detector.  A printout of the STR DNA peaks detected is created, known as an electropherogram.
5. Analysis: The electropherogram is interpreted by the DNA analyst to give meaning to what DNA was detected.  The analysis can answer questions such as: is DNA from one or multiple persons?  If it is a mixture, is the DNA from one donor in a much higher amount than others?  Is the DNA of good quality?

After these steps are completed, conclusions may be drawn as to the possible contributor(s) of the genetic material left on the evidence.  DNA is unique to each individual (with the exception of identical twins) allowing comparisons to be made between evidence items and the DNA profiles from known individuals.  In cases in which a suspect has not yet been identified, or a potential suspect has been eliminated by comparative DNA analysis, the unknown DNA profile can be entered into a database known as CODIS.

CODIS

The Combined DNA Index System (CODIS) blends forensic science and computer technology into a tool for linking violent crimes.  The Forensic Biology (DNA) Unit uses CODIS to exchange and compare DNA profiles electronically, between local, state and federal agencies, linking crimes to each other and to criminal offenders.  Analysts use CODIS to search DNA profiles obtained from evidence against DNA profiles from crime scenes, convicted offenders, and arrestees. CODIS is administrated by the Federal Bureau of Investigation and enables police from multiple jurisdictions to share leads and coordinate their investigations.

Recent Improvements in the Biology Unit

The Unit offers male specific DNA testing (Y-STR typing). This technology is especially useful for sexual assault evidence with a high ratio of female to male DNA.

The Unit uses mixture deconvolution software (STRmix™), which uses complex mathematical modeling in cases that may have previously been deemed uninterpretable.

The Unit offers free consultations for agency's cold cases. Please make and appointment and bring your case file. The Unit can help strategize the best course of DNA Analysis for your evidence. We can tell you what evidence has been consumed, should be re-analyzed, as well as whether any evidence may be amenable for a CODIS familial search and/or a genealogical search.

New Technologies Coming Soon

The Biology Unit is in a continuous state of improvement, always seeking the latest technology and methods of DNA analysis. Several instruments and software are currently in the process of validation for implementation in future casework.

The ANDE Rapid DNA instrument will allow for “sample in, profile out” analysis of reference DNA samples in as little as 90 minutes.

Comparative Evidence (Firearm and Tool Comparisons)

The Comparative Evidence Unit analyzes firearms for operability and compares bullets, cartridge cases, and shotshells to determine if they were fired from the same firearm, multiple firearms or specific firearm if submitted.  A microscopic comparison of ammunition components is done to associate a particular firearm as having fired the components. The unit also performs serial number restoration, shoeprint casework, and toolmark comparisons.

NIBIN

The Comparative Evidence Unit uses the National Integrated Ballistic Information Network (NIBIN) administered by the Bureau of Alcohol, Tobacco, Firearms, and Explosives to acquire digital images of the markings on cartridge cases recovered from a crime scene or test fires obtained from firearms. The NIBIN Program provides actionable investigative leads in a timely manner. NIBIN is the only interstate automated ballistic imaging network in operation in the United States. 

Latent Prints

Latent prints are impressions or marks produced by the raised skin, known as friction ridges, on human fingers, palms, and soles of the feet. Latent prints are among the most valuable and common types of physical evidence found at crime scenes. A variety of techniques that includes the use of chemicals, powders, lasers, alternate light sources, and other physical means, are employed in the detection and development of latent prints. The primary function of the Latent Print Unit is to develop and recover latent prints from items of evidence, compare them to known exemplars, and conduct local and national database searches.  

When latent prints are recovered or the evidence submitted is examined, analysts are able to: screen for the presence and quality of the prints; compare and identify or exclude the prints of value with the known prints of suspects or others listed for elimination purposes and decedents; or search the print via the Automated Biometric Identification System (ABIS) to produce a potential lead in the case.  The process for associating latent prints and known prints involves four phases known as Analysis, Comparison, Evaluation, and Verification, also known as ACE-V. 

1. Analysis refers to the initial information gathering process in which the analyst assesses the quality and quantity of discriminating detail present in the latent print.
2. If the latent print has sufficient information, the analyst compares the detail in the latent print to known fingerprints and palm prints.
3. In the evaluation phase, the analyst assesses the level of agreement or disagreement between the latent print and the known prints and renders a conclusion.
4. Verification is the review of the analyst’s conclusion by another qualified analyst.

The Latent Print Unit provides expert witness testimony in local and federal courts and training to law enforcement agencies on various latent print topics that include processing evidence at crime scenes and different methods to obtain high quality friction ridge detail.

Automated Biometric Identification System (ABIS)

ABIS is a sophisticated computer-based system which electronically encodes, searches, and stores the images of fingerprints and palm prints.  “Known prints” or exemplars comprise a complete set of fingerprints and palm prints taken from a known individual. Typically known prints are obtained using a Livescan device. The analysts in the Latent Print Unit use ABIS as a tool to search unknown latent prints against the known prints in the database. The ABIS software looks for details in the print to find the best match in its database.  Any potential matches or “hits” are evaluated by an analyst.  Prints that do not “hit” will continue to search in the database.

Crime Scene Response

Crime scene responders are responsible for complex crime scene investigations using various types of equipment; developing, securing, and packaging physical evidence for scientific evaluation and comparison; preparing detailed reports on the observations and activities at the scene and testifying in court regarding the findings and processing methods used at the scene. Crime scene responders are responsible for the documentation, collection, processing, and examination of physical evidence from all Law-Enforcement Involved Fatal Incidents per the County protocol. Crime scenes may be documented by the RTC360, a 3D laser scanner with the ability to quickly scan the scene with full HDR images. The resulting output file allows law enforcement and the district attorney’s office to visualize the scene as never before. 

Muir Laboratory

1960 Muir Road, 2nd Floor
Martinez, CA  94553
Phone: (925) 313-2800
Fax: (925) 313-2840
  

Drug Analysis

Examiners in the Drug Unit analyze powders, solid materials, liquids, plant material, mushrooms, blotter paper, and food items for the presence of controlled substances.  In addition, the Unit examines pharmaceutical preparations in the form of tablets, capsules, and patches.  Controlled substances are routinely screened using color tests with confirmation performed by Gas Chromatography/Mass Spectrometry (GC/MS) or Fourier Transform Infrared Spectroscopy (FTIR) coupled with Attenuated Total Reflectance (ATR).

Alcohol

The Alcohol Unit is split into blood/urine analysis and breath alcohol duties.  The blood/urine analysis consists of analyzing blood and urine samples in connection with DUI cases using Heated Headspace Gas Chromatography with Flame Ionizaion Detector (HSGC/FID). 

The breath alcohol duties include training and certifying breath test operators, responding to requests for records, providing testimony in courts of law on analysis and effects of alcohol, and maintaining the evidential breath testing instrument (Intoximeters DMT Dual Sensor) used in Contra Costa County. 

Toxicology 

The Toxicology Unit receives biological samples from law enforcement agencies for a variety of offenses, including Driving Under the Influence of Drugs (DUID) investigations.  The unit screens DUID cases for approximately 20 analytes using the Randox Biochip technology and confirms drugs by Gas Chromatography/Mass Spectrometry (GC/MS) and Liquid Chromatography/Mass Spectrometry (LC/MS) instrumentation. Drugs that cannot be analyzed in-house are sent to a reference laboratory for analysis. While statutory limits exist for alcohol none are set for other drugs; consequently, expert toxicology testimony regarding the effects of drugs on human performance and driving behavior is often necessary to establish impairment.

Property & Evidence Services

2099 Arnold Industrial, Suite D
Concord, CA  94520
Phone: (925) 646-5877

Public Property Hours: Monday - Friday, 8:30 AM to 4:30 PM

To bid on property click here.
 

Property and Evidence Services

Property and Evidence Services is responsible for the property handling of all Sheriff’s evidence, contract cities, station houses, and courts.

Proper handling includes receiving processing, packaging, tape sealing, storing, releasing and the disposition of all items taken in as evidence. This includes safekeeping and found property.  Property is responsible for protecting the integrity of its evidence from cradle to grave.

Training Opportunities

The FSD offers a wide variety of training opportunities (e.g. CSI brush-ups, DMT breath instrument, Drug Presumptive Testing, and more). For more information, please inquire at the Summit or Muir laboratory for upcoming training dates.

Customer Service

Reported results can be found on ARIES.

Management of the FSD is committed to good professional practice, to the quality of our testing, and serving our customers.

The FSD welcomes feedback from our customers. We are hopeful you will complete a testing or training survey to help us gain insight into the quality of our services and what we can do to improve. Thank you for your time. We appreciate any feedback you can share with us.

In service to our customers, the FSD will:

• Listen to comments, suggestions, and concerns in an effort to improve our services and to meet customer needs
• Cooperate with customers and their representatives to clarify their request, to provide them the information they need, and to deliver a quality work product
• Select the most appropriate test methods for the customer based on the requested service and use test methods that are valid, appropriate, and meet the needs of the customer
• Share results of testing when required to do so. Examples include sharing results with another forensic laboratory to complete a request analysis or in a technical presentation
• Send evidence to a competent external laboratory if the requested analysis cannot be performed in-house.
•  Release records when compelled to do so. Examples include complying with discovery requests, court orders, or for accreditation activities