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.
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 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 reasonably may have their DNA present at the scene of a crime such as vehicle owners, home owners/residents in the case of property crimes, 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 the source of the DNA profile developed from the evidence sample(s).
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) An estimate is made as to the amount of DNA recovered from the sample
3) Millions of copies of the DNA is made through an amplification process known as the Polymer Chain Reaction (PCR)
4) DNA is analyzed using a capillary electrophoresis genetic analyzer which separates pieces of DNA by size
5) DNA results are interpreted from the unknown evidence samples and then compared to known samples to determine whether the known individual can or cannot be the source of the DNA found in the evidence sample
6) If there is a DNA match, statistics are performed to determine the strength of the association between the evidence and reference samples Notice of Amendment of the FBI’s STR Population Data published in 1999 and 2001
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 automatically entered into the database by the Biology/DNA Detail of the LVMPD. 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 felony 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 # Reference Samples Accepted
| Homicide **
| Sexual Assault **
(including a sex assault kit)
| Crimes Against a Person
(Robbery, Kidnap, Assault, Attempted Felonies)
| Weapons Violations
(MDPP, Larceny, Explosive Devices, Recovered Property, Arson)
| Property Crimes (Burglary, Auto Theft)
Analysis on “touch” DNA evidence will not be performed on property crimes
**Although limits have been established, exceptions to policy will be made when analysis is required on additional items associated with homicides and sexual assaults and some touch DNA property crime cases (e.g. cases associated with a series). The Laboratory, in coordination with the investigators, will evaluate these situations on a case by case basis.