Blog

March 2023

Forensic Science

Texas Department of Public Safety

 

Covering 268,820 square miles of land mass and hundreds of towns and cities, the Texas DPS provides forensic services to all law enforcement agencies. With Crime Labs in Amarillo, Lubbock, Abilene, Midland, El Paso, Garland, Tyler, Waco, Austin, Houston, Corpus Christie, Laredo, and McAllen, the department is available 24/7 in support of public safety.

Forensic testing services include trace evidence (i.e., hair, fibers, paint, glass, gunshot residue, shoe prints, tire impressions, etc.), biological evidence/DNA, seized drugs, blood alcohol, fire debris, firearms, and tool marks, toxicology, friction ridge and AFIS, forensic document examinations, and digital/multimedia evidence.

Today we will introduce some of these services. As you read above, "friction ridge" may have struck you as an unfamiliar term. But, as our world changes, so do some of our descriptors. A friction ridge is what we used to call fingerprints.

Friction ridge skin refers to the skin that is present along the lengths of the fingers, across the palmar surfaces of the hand, and on the soles of the feet. The skin contains raised ridges and recessed furrows for gripping and other mechanical motions. Ridges run along the skin and may form one of three general patterns on the fingers and toes: arch, loop, or whorl. The ridge paths start and stop and may fork, and the random distribution of these features can be used for identification.  Creases appear where friction ridge skin needs to bend for grasping, and these major creases are located at the joints of the fingers and across the palmar surfaces of the hands. Smaller creases may also be present throughout the friction ridge skin. Scars will form following injury to the underlying layer of the skin, called the dermal layer, and may cause changes in the flow of the ridges.

Friction ridge skin is unique from person to person and from digit to digit. The skin is formed about six months before birth and remains persistent from infancy to death, with the exception of permanent damage or amputation. During fetal development of friction ridge skin, a combination of genetics, environment, and random factors called "developmental noise" contribute to the high variability, or uniqueness, of friction ridges. Identical twins share the same genetics and environment but have different fingerprints due to developmental noise. This term explains the unpredictable events that create a variation from person to person.

Forensic scientists in the Friction Ridge Section use chemical, physical, and optical techniques to develop, preserve, and identify friction ridge impressions left at crime scenes and on items of evidence. "Friction ridge impressions" include latent, patent, and plastic prints. Latent prints are a reproduction of the friction ridge skin left on items by the transfer of residue like sweat and oils. These prints are typically left unintentionally and require the application of a development technique to be visualized. Development techniques include, but are not limited to, superglue fuming, black powder, and fluorescent dye staining for nonporous items and ninhydrin for porous items. Additional chemicals like amido black may develop prints left in blood, also known as patent prints. Patent prints are reproductions of friction ridge skin left behind with the transfer of a material like blood, dirt, dust, paint, and other substances. These patent prints may be visible to the naked eye but may also benefit from development techniques. Plastic prints are three-dimensional reproductions of the friction ridge skin left in a pliable surface like clay. Typically these prints are photographed and may be enhanced with black powder. Once friction ridge impressions are developed, they are preserved via photography, scanning, lifting, or casting and digitally processed to be analyzed for suitability. The friction ridge forensic scientist then determines the possible orientation and anatomical source (i.e., fingerprint, palm print, or footprint) and compares the preserved print to a known exemplar print to determine if the two prints originate from the same source.  When prints are not identified, the friction ridge forensic scientists work with forensic scientists in the AFIS Section, which will be presented later.

In the meantime, stay tuned at www.thomasjnichols.com for the latest in the horrors along our border with Mexico.