FORENSIC DISCIPLINES
Alcohol
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.
Biology/DNA
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.
Firearms
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.
Alcohol