Crime Laboratory Services

Forensic Genetics

DNA Presentation
(PPT 41MB)

The Forensic Genetics Laboratory (FGL) performs serological testing of biological materials and DNA analysis of evidence submitted by law enforcement agencies in Harris County. The FGL provides testing services for felony investigations of offenses including homicides, sexual assaults, robberies, aggravated assaults, thefts, and burglaries. At the request of the Medical Examiner Service, DNA testing is also performed to assist with identification of human remains. Annually, the FGL routinely completes testing and issues reports for over 2,000 cases.

Evidence submitted for testing is screened by the FGL for the presence of biological materials using a variety of techniques and test methods. The FGL is accredited to detect and identify the presence of blood and semen using an array of color tests, immunological tests, and microscopy. The results of these serological tests are used in combination with the case information to collect samples from the evidence for further DNA testing.

Forensic DNA analysis involves a series of biochemical processes that isolate and purify DNA present on the evidence. If human DNA has been deposited on the evidence, it is amplified using a technique known as the polymerase chain reaction (PCR). This highly sensitive technique replicates specific areas of forensic interest in the human genome and allows the FGL to analyze trace amounts of DNA less than one billionth of a gram.

DNA profiles developed from evidence are interpreted by a DNA Analyst who will assess the DNA evidence to determine how many individuals may have contributed DNA. When known DNA profiles are submitted for individuals connected to the case, they are compared against the DNA evidence to evaluate if there is support that they have contributed DNA to the evidence. Eligible DNA profiles are selected for upload to the Combined DNA Index System (CODIS), a national DNA database that searches DNA profiles from crime scene evidence against DNA from convicted offenders and arrestees. The FGL has submitted more than 25,000 DNA profiles to the CODIS database. 

The Harris County Institute of Forensic Sciences Forensic Toxicology Laboratory is accredited by the ANSI National Accreditation Board, which covers compliance with the American Board of Forensic Toxicology standards.

The laboratory provides analytical services in medicolegal death investigations (postmortem analysis), driving while intoxicated (DWI) by alcohol and/or drugs, and drug-facilitated sexual assault investigations to support medical examiners, law enforcement agencies, the justice system, and other customers within Harris County.

The Institute’s Forensic Toxicology Laboratory is equipped with advanced instrumentation to perform testing services, and its toxicologists apply this wide variety of instrumental techniques in the course of their casework.

Instrumentation and testing services include:

• Headspace Gas Chromatography – Flame Ionization Detection (Headspace GC/FID) – Detects ethanol and other volatile substances
• Enzyme-Linked Immunosorbent Assay (ELISA) – Screens for common classes of drugs
• Gas Chromatography – Mass Spectrometry (GC/MS), Gas Chromatography Tandem Mass Spectrometry (GC/MS/MS) and Liquid Chromatography Tandem Mass Spectrometry (LC/MS/MS) – Confirms and quantifies drugs and their metabolites

 

The testing performed in a particular case will depend on the case type, customer request, and/or laboratory protocol. The current scope and sensitivity of screening tests may be found here.

 

Instructions for Collecting and Submitting Specimens for Toxicological Analysis
Specimen Collection

For full toxicological analysis, it is recommended that the submitting agency provide the following:

Driving While Intoxicated Cases

Drug-Facilitated Sexual Assault Cases

Failure to submit the recommended volume of blood or urine may result in incomplete testing.
 

Each specimen vial, bottle, or cup should be labeled with the following:

• Name of the individual from whom the specimen was collected
• Date and time of collection

Specimen vials, bottles, or cups should be stored inside a leak-proof container, such as a plastic bag. The samples then may be placed inside a paper specimen container, such as a cardboard box or envelope, if desired. It is acceptable to include multiple specimen vials, bottles, or cups in one specimen container if they all pertain to the same case. The specimen container should be sealed with evidence tape and must be labeled with the following:

• Initials of the individual submitting the specimen container – initials must be written across both the tape and the container
• Name of the submitting law enforcement agency
• Case number

 
To maintain the integrity of the specimen, a chain of custody should be initiated upon collection and the specimen should be refrigerated as soon as possible.
 

Submission

• Submit specimens to the Harris County Institute of Forensic Sciences Evidence Reception located at 1861 Old Spanish Trail, Houston, Texas (Click here for detailed Evidence Submission & Testing instructions).
• A completed submission form must accompany the submission. Do not attach the form to the specimen container.
• Click here to download the submission form, or request a form from the Institute’s Evidence Receiving staff during regular business hours.

DWI Testing Protocol

In suspected DWI cases, blood specimens first undergo alcohol testing. If the blood alcohol concentration (BAC) is greater than or equal to 0.100 g/100 mL, no further testing is performed. If the BAC is less than 0.100 g/100 mL, drug testing is performed. Suspected DWI cases involving a fatality will be tested for drugs, regardless of the BAC.
 

Extrapolation Testimony

Forensic toxicologists are frequently asked to provide extrapolation testimony in driving while intoxicated/driving under the influence (DWI/DUI) and drug-facilitated sexual assault cases. Retrograde extrapolation uses the measured blood alcohol concentration (BAC) to estimate the BAC at an earlier time point, typically the time of driving. Anterograde extrapolation is used to estimate either the number of standard drinks necessary to achieve a particular BAC or the reverse, estimate the BAC after a specified number of drinks.

Attorneys seeking extrapolation testimony can complete the Alcohol Calculation Request form or contact the expert reviewer listed on the Toxicology Report. Specific conditions are required to perform retrograde and anterograde calculations; therefore, calculations may not be possible if necessary information is missing and/or incomplete or if case circumstances are not conducive to extrapolation. Once completed, the written extrapolation opinion will state the basis for the opinion, including any assumptions made, and will be technically reviewed by another expert toxicologist prior to release. Please allow at least one week for the Toxicology Opinion to be emailed to the requestor.

Drug Chemistry

In accordance with Texas state statutes, the Institute’s Drug Chemistry Laboratory (DCL) analyzes suspected drug evidence seized by law enforcement agencies in Harris County. Examples include:

• Well known drugs of abuse such as marijuana, cocaine, methamphetamine, heroin, and pharmaceutical preparations
• New and emerging classes of drugs such as synthetic opioids, synthetic cannabinoids (“KUSH”, “Spice”), and synthetic cathinones (“bath salts”)
• Clandestinely manufactured tablets which appear to be legitimate pharmaceutical tablets

On average, the DCL completes approximately 6,000 cases each year. Findings are presented in analytical reports used to support the criminal justice system in Harris County.  Instrumentation used in the Drug Chemistry Laboratory includes :

• Gas Chromatograph-Flame Ionization Detector (GC-FID)
• Gas Chromatograph-Mass Spectrometer (GC-MS)
• Gas Chromatograph-Infrared Detector (GC-IRD)
• Direct Analysis in Real Time- Time of Flight (DART-TOF)
• Fourier Transform Infrared Spectrometer (FT-IR)
• Ultraviolet/Visible Spectrometer (UV-Vis)
• Microscope with digital camera attachment

Trace Evidence

The Trace Evidence Laboratory offers service for Gunshot Residue Analysis.

Gunshot residue analysis is performed utilizing Scanning Electron Microscopy/Energy Dispersive Spectrometry (SEM/EDS). The micron-sized particles from the discharge of a majority of ammunition primers can be identified by the presence of lead, barium, and antimony.

Firearms Identification

The Firearms Laboratory evaluates firearms and fired evidence components such as bullets and cartridge cases, from firearm-related incidents. When a firearm is discharged, microscopic markings are imparted on to the bullet and cartridge case. Typically, microscopic markings on recovered cartridge cases and bullets are compared to markings on test-fires made from a suspect’s firearm to determine if this is the correct firearm. If no firearm is recovered, then the cartridge cases and/or bullets are inter-compared to determine if they were fired in/from the same unknown firearm. When no suspect firearm has been submitted, often a list of potential manufacturers of firearms can be determined by laboratory examination of the cartridge case or bullet.

The Firearms Laboratory participates in the Integrated Ballistics Identification System (IBIS) / National Integrated Ballistics Information Network (NIBIN) program. IBIS / NIBIN stores and continually compares images of fired cartridge cases from crime scenes to images of other cartridge cases and / or test fires from recovered firearms, on a regional level defined by the ATF. Through the use of this technology, the Firearms Laboratory can potentially link cases that were not known to be related. If a NIBIN lead is developed, the customer will be notified and given the option to have the lead microscopically confirmed. 

Serial number restoration is another service performed by the Firearms Laboratory. This capability can assist in the identification of a weapon, even when the manufacturer’s serial number has been obliterated.

The Firearms Laboratory also performs distance determinations on the clothing a shooting victim was wearing, helping to determine the approximate distance of the victim to the firearm.