GBI Latent Prints Information

Services and Prioritization

The Latent Print Section accepts evidence from all case types but limits cases involving latent prints on suspected drugs and/or paraphernalia due to volume. Those cases are accepted only after consultation with law enforcement and prosecution officials.

Cases are prioritized based on the type of incident. Crimes against person involving injury or death take precedence over property crimes when the incoming cases are assigned. This is a general rule and exceptions are made on a case by case basis.

The section processes evidence and compares friction ridge impressions (latent prints) to submitted known samples, the GBI AFIS database and the FBI IAFIS database as warranted.

Evidence Types

In fingerprint comparisons the continuity of the ridge flow is vital to the outcome of the comparisons. Smoother surfaces usually deliver better quality impressions, but it is possible to obtain fingerprints from rough or textured surfaces depending on the specific surface. It is therefore recommended that investigators contact the section for guidance when in doubt about the suitability of items for submission.

Evidence types are categorized based on the porosity of the surfaces. Surfaces are generally divided into three types:

Porous Surfaces – These types of surfaces absorb water and water soluble deposits in the sweat very quickly after deposition.

·         Examples: Paper, checks, currency, tissue, cigarette butts, cardboard, fabrics, untreated wood, etc.

·         Probability of getting usable prints: High.

·         Best methods for developing prints: A series of processes in the following order - Visual examination, DFO (1,8-Diazafluoren-9-one), Ninhydrin (1,2,3-triketohydrindine hydrate), Physical Developer (Silver Physical developer).

Non-Porous Surfaces – These types of surfaces do not absorb the sweat. The fingerprint deposits can remain on the surface for a very long time (until degradation).

·         Examples: Glass, certain type plastics, polythene bags, metal surfaces, glazed ceramics, glossy paints, etc.

·         Probability of getting usable prints: High.

·         Best methods for developing prints: A series of processes in the following order - Visual examination, Superglue (Cyanoacrylate Ester), Fluorescent Dye Stain (for example, Rhodamine 6G), various types and colors of fingerprint powders that are mainly used when the impressions are difficult to photograph due to location on the evidence.

Semi-Porous Surfaces - These types of surfaces absorb water and water soluble deposits in the sweat slowly after deposition.

·         Examples: Certain type plastics, waxed surfaces, certain types of wall paints, papers with a glossy finish, varnished wood, etc.

·         Probability of getting usable prints: High.

·         Best methods for developing prints will depend on the specific level of porosity. Either one of the two processes or a combination of the two processes described above can be followed.

Special Surfaces

Wet surfaces - Surfaces that have been wetted before being submitted for processing (e.g., items left out in the rain, firearms discarded in lakes, etc.) generally require special handling by the section. Processes do exist to recover fingerprints on wet or previously wetted items.

·         Probability of getting usable prints: Medium to Low.

·         Best methods for developing prints:

o        Porous substrates tend to give better results with Physical Developer.

o        Non-porous substrates are usually treated with powder in suspension (e.g., Small Particle Reagent or Wet Powder).

Surfaces contaminated with blood – Fingerprints made in blood or with blood require special treatment. Fingerprints can be left by hands contaminated with blood even after the blood has dried on the hands. Some blood specific reagents will produce positive results with areas that came in contact with the dried blood. When fingerprints are left on surfaces covered with blood, they are usually visible before processing and need to be photographed with special lighting techniques before any further processing.

·         Probability of getting usable prints: High.

·         Best methods for developing prints: Blood sensitive reagents can usually be applied after the normal processing.

o        Porous substrates - both DFO and Ninhydrin will react with blood since both are protein stains. Amido Black can be used to enhance contrast.

o        Non-porous substrates - DFO can be applied on dark colored substrates and Amido Black on light colored substrates after normal processing.

Surfaces contaminated with grease or oil – Because ordinary processes are inhibited by the grease or oil, these surfaces require special treatment.

·         Examples: Disposable fast food containers and utensils

·         Probability of getting usable prints: Medium on Non-porous and Low on Porous.

·         Best methods for developing prints: Gentian Violet or Sudan Black.

Surfaces with adhesive sides

·         Examples: Various tapes including electrical tape and duct tape, labels, envelopes and stamps.

·         Probability of getting usable prints: High.

·         Best methods for developing prints: Powder in suspension techniques such as Wet Powder after the non-adhesive side has been processed with normal processes.

Thermal paper – These papers usually turn black with ordinary porous processing techniques and need special treatment.

·         Examples: Cash register receipts and fax paper.

·         Probability of getting usable prints: High.

·         Best methods for developing prints: Ruthenium Tetroxide or Dry application of Ninhydrin with no exposure to heat or humidity.

Firearms – Firearms usually require a very thorough visual examination as the substrates are often oily. Depending on the specific circumstances of the case, in some instances firearms may need to be dismantled and all individual parts processed.

· Probability of getting usable prints: Due to the variation in manufacturing protocol can range from High on some firearms to Low on others.

· Best methods for developing prints: Due to the substrate usually being metal and oily, the visual examination is vitally important. The usual non-porous process is followed on all parts that are not porous. Often the stock is untreated wood that needs to be treated with the porous process.

Cartridges and cartridge casings – Brass items need special treatment. Fingerprints have been successfully recovered from spent cartridge casings even after being exposed to the high heat from the explosion.

· Probability of getting usable prints: Medium to Low depending on the metal used for manufacturing as well as the state of corrosion of the evidence.

· Best methods for developing prints: Usual non-porous procedure with the addition of Gun Blue (Selenium Dioxide) as a last step

Latex gloves – Gloves can be successfully processed as semi-porous surfaces. They should be submitted as soon as possible in order to obtain positive processing results.

· Probability of getting usable prints: Medium to Low depending on how soon after deposition the evidence is processed.

· Best methods for developing prints: One or both of the porous and non-porous processes can be used. Recent research shows that powder in suspension yields good results, and positive results have been obtained at GBI with this process.

Print this