CSI - Crime Scene Investigator Latent Print Processing Questions and Answers 1 — Questions and Answers
Question 1: An investigator is processing a piece of untreated wood found at a crime scene. Which of the following chemical reagents is most appropriate for developing latent prints on this type of porous surface?
- Cyanoacrylate Fuming
- Amido Black
- Ninhydrin (Correct answer)
- Small Particle Reagent (SPR)
Correct answer: Ninhydrin
Ninhydrin is the most effective reagent for developing latent prints on porous surfaces like untreated wood, paper, and cardboard. It reacts with the amino acids present in fingerprint residue to produce a purple-colored print called Ruhemann's purple. Cyanoacrylate fuming is used for non-porous surfaces, Amido Black is a protein stain used for prints in blood, and Small Particle Reagent is primarily used for wet, non-porous surfaces.
Question 2: A CSI is preparing to use cyanoacrylate fuming to process a plastic bottle for latent prints. To ensure optimal development, which two environmental factors within the fuming chamber are most critical to control?
- Temperature and Air Pressure
- Humidity and Temperature (Correct answer)
- Light and Airflow
- Time and Static Electricity
Correct answer: Humidity and Temperature
Effective polymerization of cyanoacrylate (super glue) fumes onto latent print residue is highly dependent on controlled levels of humidity and heat. Heat is used to vaporize the cyanoacrylate, and moisture in the air (humidity) is necessary for the polymerization reaction to occur, which makes the white print visible. Optimal humidity is often cited as being between 70-80%. While fuming time is a variable, it is dictated by the primary factors of heat and humidity.
Question 3: Which of the following describes the primary mechanism by which Small Particle Reagent (SPR) develops latent prints?
- Reacts with amino acids to form a colored compound.
- Stains protein residues in the print.
- Fumes adhere to moisture and polymerize on the ridges.
- Fine particles physically adhere to the fatty components of the print residue. (Correct answer)
Correct answer: Fine particles physically adhere to the fatty components of the print residue.
Small Particle Reagent (SPR) consists of a suspension of fine, insoluble particles (like molybdenum disulfide) in a detergent solution. These particles physically adhere to the lipids and fatty components present in latent print residue. This method is particularly effective on wet or previously wet non-porous surfaces.
Question 4: A CSI must process a ransom note written on standard copy paper. To maximize the chances of developing prints, what is the correct sequence for applying chemical treatments?
- Ninhydrin, then Cyanoacrylate Fuming
- Physical Developer, then Ninhydrin
- Iodine Fuming, then DFO, then Ninhydrin (Correct answer)
- Cyanoacrylate Fuming, then Fingerprint Powder
Correct answer: Iodine Fuming, then DFO, then Ninhydrin
For porous surfaces like paper, a specific sequence is followed to avoid destroying evidence. The generally accepted sequence begins with less destructive methods. A common and effective sequence is Iodine Fuming (reacts with oils), followed by DFO (reacts with amino acids, requires a light source), and then Ninhydrin (also reacts with amino acids). This order ensures that subsequent processes do not interfere with or wash away the residue needed for the earlier ones.
Question 5: At a crime scene, a CSI finds a vehicle that was recently driven through the rain. A latent print may be present on the wet, painted exterior door. Which processing technique would be most suitable for this situation?
- Black Powder Dusting
- Small Particle Reagent (SPR) (Correct answer)
- Cyanoacrylate Fuming
- Iodine Fuming
Correct answer: Small Particle Reagent (SPR)
Small Particle Reagent (SPR) is specifically designed for developing latent prints on wet or previously wet, non-porous surfaces such as a car door. The fine particles in the SPR suspension adhere to the fatty residues of the print, which are not water-soluble. Using standard powder on a wet surface would turn it into a paste and destroy the print. Cyanoacrylate and Iodine fuming are not effective on wet surfaces.
Question 6: Thermal paper, such as a store receipt, is a difficult surface for latent print development because processing can cause the entire surface to darken. Which of the following methods has been shown to be effective for developing prints on thermal paper WITHOUT using a chemical solvent?
- Ninhydrin in Acetone
- Physical Developer
- Application of low-temperature heat (Correct answer)
- Amido Black Staining
Correct answer: Application of low-temperature heat
Research has shown that the controlled application of low-temperature heat, for example from a hairdryer or laboratory oven, can develop latent prints on thermal paper. This method works without chemical solvents that often cause the paper's heat-sensitive coating to activate and turn black, which would obscure any prints. Ninhydrin and Physical Developer involve wet chemical processes that can ruin the thermal paper. Amido Black is for prints in blood.
CSI - Crime Scene Investigator Latent Print Processing Questions and Answers 1
An investigator is processing a piece of untreated wood found at a crime scene.
Which of the following chemical reagents is most appropriate for developing latent prints on this type of porous surface?