Sheriff's Office

Biology Unit

Biology Unit (Primary Examination, DNA Casework, and DNA Database Sections)

Lisa Smyth-Roam Ph.D., Supervising Criminalist
Main Phone: (775) 328-2898

Steve Gresko, CODIS Administrator / Supervising Criminalist
Main Phone: (775) 328-2851

Laura Dickson, Supervising Criminalist
Main Phone: (775) 328-8729

Primary Examination Section:

The Washoe County Sheriff’s Office Primary Examination section is responsible for a wide variety of examinations including laboratory tests to locate and identify physiological fluid stains. Specifically, this section can examine evidentiary items for the presence of blood, semen, and/or saliva. Important physiological fluid stains are those that either provide a link (e.g., victim to suspect, suspect to scene) or provide an element of the crime (e.g., finding semen on a vaginal swab in a sexual assault case). With this in mind, certain items of evidence may be excluded from the initial examination.

Sometimes physiological fluid stains are visible to the naked eye. However, special lighting or chemical processing techniques may be employed to search an item of evidence or a crime scene when staining is not readily visible. Luminol is a chemical that can be used to detect trace amounts of blood. It is particularly useful in cases where deliberate cleaning attempts have been made to conceal blood staining at a crime scene. Luminol is applied as a spray so large areas can be quickly screened for blood. When luminol comes into contact with blood it results in the production of light which is visible as a bluish-green glow. Near total darkness is required for this test to be performed. Luminol is relatively non-destructive to the surfaces on which it is applied and to any blood that may be present.

Once a suspected physiological fluid stain is located, it is examined with a quick and sensitive, but non-specific presumptive test to determine if it could be blood, semen, or saliva. If a positive result for the presumptive presence of one of these fluids is obtained then the stain may undergo confirmatory testing and/or be collected for further examination in the DNA Casework Section.


The following stain indication chemicals and techniques may be utilized:

Kastle-Meyer test, Luminol, ABAcard HemaTrace test, Acid Phosphatase test, Microscopic Examination, ABAcard p30 test, RSID-Saliva test and Hemastix test.

Additional physiological fluid stains such as fecal matter, urine, and stomach contents (i.e., vomit) are not examined in the WCSO Primary Examination Section. Should it be necessary for items of evidence to be tested for fluids such as these, please contact the FSD for referral to an outside agency.

In addition to physiological fluid stains, this Section also examines evidentiary items for the presence of hairs. Hair examinations serve best to aid in associating an individual with a location or another individual that they deny being in contact with. Laboratory examination of hairs collected from items or crime scenes begins with a determination of the species of origin, i.e., animal versus human. The source of human hairs in terms of body area origin can also sometimes be determined, i.e., head versus pubic. Furthermore, in some cases it may be possible to determine whether a hair has been forcibly removed. If a human hair is located and it has root tissue present then that root can be collected for further examination in the DNA Casework Section. Microscopic hair comparisons to determine the source of the hair are not performed.


Physiological fluid stains should be considered as potential biohazards and treated as such. Protective gear should be worn when appropriate for the collection of stains at a scene. Gloves should be changed frequently to protect evidence from possible contamination when moving from area to area within a scene.


Items should not be packaged while still wet or moist. Thoroughly dry all stains and then place the evidence in paper bags, envelopes, or boxes. Please DO NOT place evidentiary samples in plastic bags or containers as this promotes DNA degradation.


Kits for collection of evidence from victims and suspects involved in sexual assault cases are available from the FSD free of charge. These kits are distributed to law enforcement agencies and hospitals upon request.

DNA Casework Section

DNA stands for deoxyribonucleic acid. It is the fundamental building block of life found in almost every cell of the body.  Half of our DNA is inherited from our mother, while the other half is inherited from our father. A person will have the same DNA in every cell of their body. For example, the DNA in a person’s blood cells will be the same as the DNA in their saliva and skin cells. There are two main types of DNA examined in forensic DNA analysis, nuclear and mitochondrial DNA. Nuclear DNA is the type of DNA that is examined in the Washoe County Sheriff’s Office (WCSO) DNA Casework/Database Sections.

The DNA Casework Section performs analysis on human biological material such as blood, semen, hair roots, saliva and tissue. This analysis can assist in identifying the source of the biological material and provides investigative leads in homicide, sexual assault, burglary and other cases where biological evidence is obtained.



The DNA analysis technique currently used in the WCSO DNA Casework/Database Sections is the polymerase chain reaction (PCR). As a result of the PCR process, millions of identical copies of areas on the DNA called Short Tandem Repeats (STR) are created. These STR areas are highly variable among individuals allowing us to generate a DNA profile that is unique to an individual, except for identical twins. This technique radically altered DNA testing by significantly decreasing the amount of DNA required to produce a DNA profile. Once a DNA profile is generated from items of evidence, e.g., a blood stain, we will compare this DNA profile to the DNA profile obtained from a known individual usually the victim and suspect. A cheek swab or blood sample from a known individual is called a reference sample. If the DNA profile from the evidence and the reference sample are the same, we can then provide a determination of the statistical significance of the match.

The following kits are used: Plexor HY® Human DNA Quantification Kit, PowerPlex 16® HS PCR Amplification Kit, and QIAamp DNA Mini Kit.


When the DNA profile from the evidence and the reference sample are the same and the estimated frequency of this matching DNA profile is rarer than 1 in 8 trillion individuals, the report may read as follows: “Based upon these results, it is reasonable to conclude that John Doe is the source of this DNA profile.”

Conversely, if the estimated frequency of the matching DNA profile is not rarer than 1 in 8 trillion individuals, the report may read as follows: “Based upon these results, John Doe cannot be excluded as the source of this DNA profile.” The actual frequency of occurrence will be included.

When the DNA profile from the evidence and the reference sample are different, then the report may read as follows: “John Doe is excluded as the source of the DNA profile obtained from the evidence.” 


The WCSO DNA Casework/Database Sections also provides Y STR testing. Utilizing the same PCR technique as above, the STR target areas are now specifically located on the Y chromosome. Females have two X chromosomes while males have an X and a Y chromosome. Therefore, Y STR analysis examines only the male portion of DNA. Y STR’s are particularly useful in instances where the female portion of DNA largely outweighs the male portion of DNA, e.g., a vaginal swab from a female sexually assaulted by a vasectomized male. Y STR analysis is also useful in missing person cases.  All paternally related males will have the same Y STR DNA profile since the Y chromosome is inherited from the biological father.

The following kits are used: Plexor HY® Human DNA Quantification Kit, QIAamp DNA Mini Kit, and AmpFâ„“STR® Yfiler® PCR Amplification Kit

If a matching male Y STR DNA profile is observed, the report may read as follows: “Based upon these results, John Doe or any of his male paternal biological relatives cannot be excluded as the source of the male DNA obtained from the evidence.”  A statistic will also be provided.


In cases where the biological evidence may be degraded or too small in quantity for the STR analysis described above, mitochondrial DNA (mtDNA) analysis can be used. MtDNA analysis is advantageous because mtDNA is far more abundant than nuclear DNA. The WCSO DNA Casework/Database Sections do not provide this type of test. However, the FBI has developed regional mtDNA testing laboratories to which cases can be sent free of charge for mtDNA analysis. MtDNA is particularly useful in cold cases; missing person cases; and cases in which hairs, bones, and/or teeth are the only evidence found. All maternally related individuals will have the same mtDNA profile since mtDNA is inherited from the biological mother.


Typical items of evidence collected from a crime scene may include but are not limited to the following: bloodstains, saliva stains, and semen stains deposited on virtually any surface; genital, vaginal, cervical, rectal, and anal samples collected on swabs or gauze; toothbrushes; food items; pieces of human tissue or skin; fetal tissue; fingernail scrapings/swabbings; forcefully removed hairs; skin cells deposited on drinking containers or handled items; and clothing.

Biological materials that may not result in successful DNA analysis include stomach contents (including vomit), urine, feces, and adipose (fat) tissue. In addition, tissue samples preserved in formaldehyde (formalin) for more than three days are not suitable for DNA analysis.


When submitting evidence, thoroughly dry all stains and then place the evidence in paper bags, envelopes, or boxes. DO NOT place evidentiary samples in plastic bags or containers as this promotes DNA degradation. Avoid contamination by wearing protective gear and changing gloves as necessary. Do not talk over the evidence without a mask on.  Soil and feces contamination and extreme exposure to sunlight or humidity are among the most effective ways to degrade DNA.

All evidentiary samples and appropriate reference standards associated with a case must be submitted to the laboratory before testing can begin. Comparison of DNA profiles cannot be made without the appropriate reference standards (victim and suspect). In cases where there is an unknown suspect and the victim cannot be associated with the evidence, unknown DNA profiles may be searched against the State and National DNA databases. Additionally, prior to beginning DNA analysis, some cases may require a stipulation to consume the evidence due to the size or nature of the sample (i.e., a hair root). This may be obtained from the court or case prosecutor.

When submitting items for DNA analysis please take into account the following sample limits:

• Homicide (up to 15 evidentiary samples and 10 reference standards)

• Sexual Crimes (with presence of sperm up to 3 evidentiary samples and 5 reference standards)

• Sexual Crimes (absence of sperm up to 5 evidentiary samples and 5 reference standards)

• Crimes against a person (up to 4 evidentiary samples and 5 reference standards)

• Property crimes (up to 2 evidentiary samples and 5 reference standards)

DNA analysis is not performed on the following types of cases: weapons violations, possession of stolen property, found property, vandalism, controlled substances, and larceny.

DNA analysis on bones or teeth is not available through the Forensic Science Division.  The FSD may facilitate the submittal to another lab for testing. 

DNA Database Section
This unit, with the assistance of the FBI, operates a statewide computerized DNA database of convicted offenders, forensic unknowns and missing persons. This database assists law enforcement in unsolved cases. The DNA profile from biological material left behind at a crime scene by a suspect can be searched against the state and national DNA databases. This may assist law enforcement in apprehending a suspect.

The state of Nevada requires anyone convicted of a felony and anyone arrested for a felony to provide a DNA sample for inclusion into the DNA database. Refer to NRS 176.0911, NRS 176.0913, and NRS 176.0915.

The FBI, in conjunction with the fifty states, established a computer software program called the Combined DNA Index System (CODIS). This software allows Local, State, and National DNA databases to compare DNA profiles electronically. CODIS acts as a repository of DNA profiles from convicted offenders, unsolved crime scene evidence, missing persons, unidentified human remains and volunteers. CODIS can provide an investigative lead by linking serial crimes to each other and identifying suspects by matching DNA profiles from crime scenes with profiles from convicted offenders. The WCSO DNA Analysis Unit has provided investigative leads in homicides, sexual assaults, burglaries, robberies, auto thefts, home invasions, and missing person cases.

The Local, State, and National DNA databases do not allow DNA profiles from victims. All unknown DNA profiles must be compared to any associated victim or non-suspect DNA profiles for elimination purposes before entry into CODIS is allowed. Therefore, it is required to submit victim reference standards along with the evidence. Alternatively, case information stating that the victim can in no way be associated with the evidence may be provided.

All DNA profiles are entered into the State DNA database.  For more information on the extent of the entry into the national database is determined by the CODIS system. 

For more information on the CODIS System, visit the FBI’s website at the following address:


Convicted offender samples are sent to an approved and accredited subcontractor for analysis.  Subcontractor analysis is 100% technically reviewed by the WCSO Biology Unit prior to entry in the DNA database (CODIS).