Crime scene investigators often follow a two-phase process when searching for fingerprints.
- First they look for patent and plastic prints since they are visible. Often times, a flashlight is used during this phase.
- The second phase involves a blind search for latent prints.
The process is concerned with recognition, examination, identification, individualization, and evaluation.
Systematic Approach To Developing Latent Fingerprints on Different Surfaces
Systematic Approach for Developing Bloody Fingerprints
Systematic Approach For Developing Latent Fingerprints On Greasy Or Waxy Surfaces
Systematic Approach for Developing Latent Fingerprints on Adhesive Tapes
Development Of Latent Fingerprints On Various Surfaces By Different Methods
Crime Scene Investigators often use chemical methods to locate the print such as iodine fuming, silver nitrate, or ninhydrin.
When one of these chemicals comes into contact with the chemicals present in the fingerprint residue (natural oils, fats), the print become visual.
Iodine fuming takes place in a fuming chamber. The process works by heating up solid crystal iodine which creates vapors that adhere to the oily residue of print, producing a brown colored print.
It must be photographed quickly because Print fades quickly after the fuming takes place.
Silver nitrate, when exposed to latent prints, reacts with the chloride of the salt molecules found in print residue, forming silver chloride. When it’s exposed to ultraviolet light, silver chloride turns black or brown,which make the print visible.
This method works particularly well on impressions left in cardboard and paper-like surfaces.
The object on which the print is located can be dipped in or sprayed with a ninhydrin solution, which reacts with the oils in the print’s residue to create a bluish print.
Laser Illumination Creates A Contrast Between The Print And The Surface Which Exposes The Print.
Systematic Approach For Developing Latent Fingerprints On Porous Surfaces, Including Paper (Porous Surfaces…..)
A powder technique is usually used to identify latent prints on nonporous surfaces such as glass, marble, metal, plastic, and finished wood.
When powder is distributed on the surface, it adheres to the residue deposited from the finger’s touch, allowing investigators to find the print.
Magnetic Powder Technique
Often times, to avoid smudging the print, a magnetic powder technique is used in which the powder is poured on the surface and then spread evenly over the surface using a magnetic force.
Superglue fuming is a chemical process that exposes and fixes fingerprints on a nonporous surface.
In the lab, An airtight tank, known as a fuming chamber use to heat up superglue (liquid cyanoacrylate) which releases gases that adhere to the oily residue of print, thereby creating an image of the fingerprint.
At the crime scene, investigators may use a handheld wand that heats up superglue and a florescent dye.
Systematic Approach For Developing Latent Fingerprints On Nonporous Surfaces
Locating and identifying fingerprints left on human skin is incredibly difficult. According to Scientific Evidence, the first major obstacle is finding the print since the oily residue left by fingers that creates the fingerprint itself is often present on human skin, making it difficult to create a contrast between the surface (skin) and the print.
Two hours is the maximum amount of time that a print on skin may be viable.
Amido Black, a non-specific protein stain that reacts with any protein present, is typically used for developing or enhancing bloody impressions on human skin.
Surfaces that are not flat or have a rough surface, such as a painting with brush strokes or a golf ball will make the process of identifying and collecting fingerprints more difficult, but not impossible.
Accu Trans, a liquid casting compound, can be used to lift powdered latent prints from rough, textured or curved surfaces.
Other Methods For Development of Fingerprints
Involves the illumination of fingerprints due to fluorescing particles picked up during everyday life from paints, inks and oil.
It can be used on painted walls, metals, plastic, rubber, cloth and wood.
The fingerprint is developed by first evaporating a thin layer of gold onto the specimen, followed by a layer of Cadmium which fills in the print and provides a contrast.
Certain bacteria, for example “Acinetobacter Calciacatieus”, can be used to develop prints on valuable oil paintings.
The bacteria in a nutrient gel are pasted onto the surface of the painting, making the print visible as they multiply. The gel can then simply be wiped off, leaving the painting unaffected.
Radioactive atoms are incorporated into the fingerprint by placing the piece of fabric into a container containing radioactive gases, such as Iodine or Sulphur Dioxide, at a humidity of less than 50%. The fabric is then put into contact with photographic film, and the radioactive atoms cause a picture to become clear.
Alternate Light Source (ALS)
These are laser or LED devices that emit a particular wavelength, or spectrum, of light.
For example, investigators may use a blue light with an orange filter to find latent prints on desks, chairs, computer equipment or other objects at the scene of a break-in.