Biology/DNA

The Biology/DNA Detail is divided into two units with two distinct areas of focus: the Casework Unit and the CODIS/Database Unit. The Casework Unit provides forensic DNA services to the southern Nevada community through the analysis of evidence associated with violent offenses, property crimes, and non-violent crimes.  The CODIS/Database Unit operates and administers the southern Nevada Local DNA Index System, to include the processing of database samples for entry into the database.

Casework Unit

The Casework Unit is responsible for processing evidence from homicides, sexual assaults, robberies, burglaries, auto thefts, weapons violation cases, and many other crime types.  DNA may be found on a variety of evidence items such as clothing, weapons, smoked cigarettes, used condoms, fingernails, bottles, cans, cups, ligatures, and glasses, which are commonly left behind at crime scenes.   DNA originates from various sources within the body to include blood, saliva, seminal fluid, and skin cells.  Any probative biological sample that has been stored dry or frozen, regardless of age, may be considered for DNA analysis.  

In order to compare unknown DNA profiles obtained from evidentiary items, DNA analysis requires reference standards from victims, suspects, or other individuals who may reasonably have their DNA present at the scene of a crime, such as homeowners/residents in the case of property crimes, vehicle owners, consensual sex partners, or anyone who may have previously handled the evidence items.  A reference standard consists of a swabbing taken from the inside of a known individual's cheeks, known as a buccal swab.  A DNA profile is then developed from this sample and used for comparison to determine whether or a not a particular individual could be a contributor to the DNA profile developed from the evidence sample.

Several basic steps are performed during the DNA analysis process regardless of the type of sample being processed.  This general procedure includes:

1. DNA is removed from cells through the addition of chemicals.
2. The amount of DNA (including male-specific DNA) recovered from the sample is measured.
3. Millions of copies of the DNA are made through an amplification process known as Polymerase Chain Reaction (PCR).
4. DNA is analyzed using a capillary electrophoresis genetic analyzer which separates pieces of DNA by their size.
5. DNA results from the evidence samples are analyzed to determine if they are suitable for comparison to reference standards.

When an evidence sample is deemed suitable for comparison, a statistic is calculated to determine the strength of association between the evidence and reference standard. This statistic indicates whether there is support for the individual being a contributor of the DNA found in the evidence sample.

DNA profiles obtained from items of evidence believed to be from the suspect may be entered in the Forensic Index of the Combined DNA Index System (CODIS).  CODIS is operated, supported, and managed by the Federal Bureau of Investigation (FBI). The purpose of CODIS is to aid investigations by providing leads through the association of DNA profiles to one another.  Names, social security numbers, ID numbers, and other personally identifiable information are not stored in CODIS.  DNA profiles obtained from forensic cases that are eligible for CODIS entry are entered into the database by the Casework Unit of the LVMPD Biology/DNA Detail.  All profiles contained in the database are searched against one another on a weekly basis and any potential matches that occur are known as "hits".  CODIS hits may link forensic cases to other forensic cases and/or link convicted offenders or arrestees to forensic cases.  All pertinent CODIS hit information is disseminated directly to the investigating agent(s) by the Biology/DNA Detail.

Sample Limitations Policy
In order to ensure analysis of the most probative evidence, to meet casework demands, and to provide for the responsible use of resources, the Forensic Laboratory has implemented sample limitations in the Biology/DNA Detail.  For details regarding the sample limitation policy, please refer to the following table: 

Crime Category	Maximum # of Evidence Items Accepted	Maximum # of DNA Reference Samples Accepted
Homicide	15	10
Sexual Assault	3 (including Sexual Assault Kit*)	5
Crimes Against a Person (Robbery, Kidnap, Assault, Attempted Felonies)	5	5
Weapons Violations	4	5
Other Crimes (Explosive Devices, Recovered Property, Arson, and Fraud)	2	5
Property Crimes (Burglary, Auto Theft, Recovered Stolen Vehicles, Malicious Destruction of Private Property, and Larceny/Grand Larceny) DNA Analysis will not be performed on "touch" evidence from property crimes or evidence containing possible "saliva" from recovered stolen vehicles, unless a vehicle was used in another felony crime.	2	5

 

Although limits have been established, exceptions to the policy may will be made when analysis is required on additional items. The Forensic Laboratory, in coordination with the investigators, will evaluate these situations on a case-by-case basis.

*All Sexual Assault Kits (SAKs) impounded at the Evidence Vault will be analyzed by the Forensic Laboratory unless the victim indicates in writing that a crime did not occur. The Forensic Laboratory will automatically perform DNA testing on SAKs without a formal Forensic Laboratory Examination Request. The SAKs may be processed in-house or outsourced to a private DNA laboratory as needed. In the event the investigator needs items external to the SAK tested for DNA such as bedding, sheets, or clothing, a Forensic Laboratory Examination Request must be submitted.  The SAK and any associated buccal swabs will be processed first to obtain a Combined DNA Index System (CODIS)-eligible profile. In the event the SAK yields a CODIS-eligible profile, all additional requested items of evidence external to the SAK (e.g., bedding or clothing) will not be examined. In the event analysis of additional items are necessary for court proceedings, an email may be sent to the Forensic Laboratory requesting analysis of the unexamined items.  If the investigator requires specialized DNA testing performed on the SAK or other evidence items (such as genetic genealogy), a Forensic Laboratory Examination Request must be submitted. In the event a victim indicates in writing that a crime did not occur, the investigator must notify the Biology/DNA Detail so DNA testing is not unnecessarily conducted.

CODIS/Database Unit

The CODIS/Database Unit is responsible for processing buccal swab samples collected in southern Nevada as a result of convictions for felony and most gross misdemeanor offenses, arrests for felony charges where probable cause is found, and registration requirements for sexual offenders.   These specimens are collected from several prisons and law enforcement agencies throughout southern Nevada, funneled to the LVMPD for DNA processing, and entered into the Convicted Offender or Arrestee Indices of CODIS in accordance with Nevada Revised Statutes. 

The LVMPD operates a Local DNA Index System (LDIS), which was established in 2000, and currently contains over 190,000 offender, arrestee, and forensic profiles.   Nevada's State DNA Index System (SDIS) currently contains over 245,000 DNA profiles and has aided over 7,000 investigations since it was established in the mid 1990's.