Bloodstain Pattern Analysis
  Computer Forensics
  Controlled Substances Analysis/Narcotics
  Crime Scene Investigation
  Questioned Documents
  Latent Print Development
  Latent Print Examiner
  Trace Evidence


The Alcohol Unit analyzes fluid samples to determine the concentration of alcohol by means of gas chromatography. The majority of the samples are blood samples related to Driving Under the Influence (DUI) suspicion, but the lab also receive samples related to other criminal offenses.  Some of the other types of samples received are jail produced alcoholic beverages, sealed alcoholic beverage containers related to sale of alcohol to minors and opened containers that may be related to violations of Alcoholic Beverage Commission.

The unit manages the evidentiary breath testing program in the County of San Diego, providing maintenance, operator training, repairs, and technical support of the Intoximeters« Intox EC/IR instruments that are deployed throughout the county. About 8,000 breath tests are reviewed each year for compliance with State regulations and laboratory policies.

One of the unit's main responsibilities is to provide expert witness testimony on the analysis of alcohol and the effects of alcohol in the human body as it relates to driving. The alcohol unit  averages about 3-4 DUI cases per week.

The unit also serves as a hub for the shipment of samples that require toxicology analysis since the laboratory does not perform this type of analysis in house.


The Biology Unit is often referred as the "DNA Unit" because DNA technology is applied to help solve crimes.  Specifically, the unit is responsible for analysis of evidence from crimes against persons and property, with the purpose of identifying and individualizing biological materials found as part of that evidence. Commonly examined materials include blood, semen, saliva, tissues and bone.  The Biology/DNA Section has the ability to identify body fluids and their species of origin and to determine the DNA profile from evidentiary items. They testify to these results in criminal trials.

The Biology Unit works closely with detectives investigating crimes. They also  educate law enforcement and the public about their work and participate in community events and programs, such as the academy training of Sheriff's cadets, the county Sexual Assault Response Team training program, law enforcement training in biological evidence collection and school presentations.

The San Diego Sheriff's Crime Lab is now a part of the national DNA database CODIS (Combined DNA Index System). DNA profiles are submitted from evidence into CODIS, so that they may be searched against DNA samples from other labs in the county, state and nation. DNA profiles are also searched against samples that are taken from convicted offenders. With the implementation of Proposition 69: DNA Fingerprint, Unsolved Crime & Innocence Protection Act, the Forensic Biology Section has become actively involved in educating and distributing the necessary information and equipment to collect the samples necessary to build the CODIS database.

Bloodstain Pattern Analysis

Bloodstain pattern analysis is the application of scientific principles and techniques to the analysis of bloodstains found at crime scenes or observed on evidence submitted to the laboratory. It involves the recognition and study of the physical characteristics of bloodstains and patterns as a function of origin, flight paths, force, and sequence. The ultimate result can be a reconstruction of the chain of events involving bloodshed.

Things that can sometimes be determined from a Bloodstain Pattern Analysis include:

▪  Minimum number of blows on a source of blood
▪  Locations of areas of impact on blood
▪  Directions of swings of bloody objects
▪  Directions of movements of bloody objects
▪  Relative positions of people and objects
▪  Sequence of events
▪  Who or what could or could not have been present, and
▪  What actions could or could not have occurred in the:
   ▪  Suspect’s statements
   ▪  Victim’s statements
   ▪  Witness’ statements

Bloodstain Pattern Analysts prefer to attend the scene. Training is available for law enforcement personnel who are not sure when to ask an expert to come to a scene. If you would like to arrange to have this training for your agency, please contact the Crime Laboratory.

Computer Forensics

The San Diego Sheriff's Crime Lab partners with the San Diego Regional Computer Forensics Laboratory in providing full service computer forensics.

Controlled Substances Analysis/Narcotics

The Controlled Substances Analysis/Narcotics Unit tests unknown powders, pills, plant materials and liquids to determine if they contain any controlled substances, as defined by federal and California laws. The unit uses a variety of techniques ranging from basic wet chemistry, such as thin layer chromatography to sophisticated instrumentation such as the Gas Chromatograph Mass Spectrometer (GCMS).

The unit is at the forefront of continuing education on what types of drugs may be available. Analysts attend training provided by the Drug Enforcement Agency (DEA) and the California Narcotics Officers Association (CNOA).

The unit is also responsible for providing expert witness testimony on cases worked in the lab.  The unit provides training in narcotics presumptive testing and proper handling and packaging of suspected drugs for law enforcement officers in the field.

Crime Scene Investigation

The Crime Scene Investigation (CSI) Unit is responsible for examining the scene of a crime, documenting the conditions present, and providing investigators, attorneys and ultimately the jury, with an accurate depiction of the locations and relationships of items located within the scene. They determine the relevance of items within the scene and the evidentiary potential of the items as related to the crime under investigation. The unit preserves and collects the items deemed potential evidence, as well as process the items of evidence that are not removable from the scene. The evidence is delivered to the Crime Lab for forensic examination, and a report is prepared detailing the actions taken at the crime scene. The purpose of the CSI Unit is to help establish what occurred and to identify the responsible person. The ability to recognize and properly collect physical evidence is critical to solving violent crimes.

Typical services include photography, videotaping, crime scene sketch preparation, evidence collection, latent print development, blood enhancement, bloodstain pattern analysis, trajectory determination, shooting reconstruction, crime scene reconstruction and expert testimony.

Questioned Document

The Questioned Documents Unit uses scientific principles for the examination and comparison of signatures, handwriting and hand printing, but the section does not determine personality profiles based on handwriting style.  The unit can detect, restore and decipher indented, erased, altered and obliterated writings, including burned and charred documents. Documents generated from printers, typewriters and photocopiers can be associated with their source. Examinations are conducted to resolve questions concerning the age, origin, content, or authenticity of documents. Document examiners prepare visual aids for court displays and testify in court when required.

The unit is equipped with microscopes, cameras (film and digital), an electrostatic detection apparatus (ESDA) to detect indented writing, and a video spectral comparator-2000 to examine inks and papers with different lighting techniques.

Upon request, training is provided for all law enforcement personnel who use the services of the Questioned Document Section.


The Firearms Analysis Unit provides technical expertise in the analysis and interpretation of firearms-related evidence.  They examine firearms, discharged bullets, cartridge cases, shotgun shells and ammunition. Serial number restorations are performed using various physical and chemical methods. Garments are microscopically examined to detect firearm discharge residues (GSR) and to approximate the distance from a target at which a weapon was fired.  The results of these microscopic comparisons and chemical evaluations are summarized in written reports and presented in courtroom testimony.

The unit is often called out to special cases to provide technical crime scene assistance and expertise in the projectile path analysis, reconstruction and collection of firearms-related evidence.

The unit maintains an Integrated Ballistics Identification System (IBIS), which can link unrelated crimes through the input of firearm evidence into a national ballistics database.

The unit routinely provides forensic services for local, state and federal agencies. Training seminars are provided for investigators, attorneys and other forensic specialists.

Latent Print Development

Detecting and developing latent fingerprints from a crime scene are critical functions in a criminal investigation. Latent print development is performed in every kind of case—from a petty theft at a convenience store to murder. It is as much art as it is science. And it is done by field deputies and patrol officers, by criminal investigators and forensic professionals and even by trainees, student interns taking their first step into the world of criminal investigations and forensic science.

Much of the work of developing latent fingerprints is done in the field by Sheriff’s deputies or city police officers. They are called to the scene of a burglary or robbery and they search for fingerprints at the site of the crime or on objects at the crime scene. The usual technique is to dust with black powder and then lift the print with tape onto a card. That card becomes part of the evidence in the case and can be compared to the prints of a suspect. When items of evidence are seized and preserved for fingerprinting, the Latent Print Development Section takes over, looking latent prints using a variety of techniques. The lead of the section is a Latent Fingerprint Examiner.

Fingerprint evidence is found on objects that have been touched. Such prints may or may not be visible. Visible prints are those showing ridge detail made by fingers contaminated with substances such as blood, ink, grease or dirt; or are made when fingerprints are pressed into plastic like putty or tar. The majority of fingerprint evidence is not visible, and these prints are called latent prints. Developing the latent print to become visible requires some chemical or physical process.

The ideal surface to obtain fingerprint evidence is a smooth, nonporous object like glass. However, through the use of powders, chemicals, and lasers, fingerprint evidence can be found on a wide variety of surfaces.

Once a print is developed it can be compared to a known suspect or it can be submitted to fingerprint databases for automated searches—to determine if the latent print matches and help solve the crime.

Latent Print Examiner

The Automated Latent Print Section, ALPS, where individuals are known as latent print examiners, specializes in identification through examination of friction ridge skin impressions. This is an applied science based upon the foundation of uniqueness and permanence of ridge detail found on fingers and palms.

Evidence for the ALPS unit consists of lifts or photographs of prints from crimes scenes or evidence items, and major case prints from known individuals or suspects. Most prints from crime scenes are “latent” or cannot be seen, and the ALPS unit relies on the expertise of the Latent Print Development Section (see LPD Section description) to visualize the prints.

The two most common analyses for the ALPS unit consists of comparing the friction ridge detail of prints from crime scenes to the prints of known suspects, or entering prints without suspects into the Automated Fingerprint Identification System (AFIS).

The AFIS system is a powerful tool which consists of a network of local, state and federal database depositories which house the know prints of persons previously arrested.
This system often enables examiners to provide suspects names to cases where they may not have been any suspects yet developed.

If a suspect is developed through the use of the AFIS system, the skills of a trained latent print examiner are still necessary to make the final confirmation or elimination of a suspect. All analytical conclusions are confirmed by two examiners independently.

Since our agency is a regional crime laboratory, we also assist other agencies with their fingerprint evidence. In addition, our examiners are available for call out assistance at crime scenes.

Trace Evidence

The Trace Analysis Unit is consists of Hairs, Fibers, Glass, Paint, Fire Debris, Explosives, Impressions, and Miscellaneous.  The unit examines specific types of trace evidence like fibers and explosives.  The following instruments are used:  gas chromatograph mass spectrometer, an FTIR microscope, a scanning electron microscope with an x-ray detector, and a GRIM while learning techniques like basic and advanced microscopy, microchemistry, and capillary electrophoresis.