CSI Latent Print Processing 3 — Questions and Answers
Question 1: Which powder is recommended for developing latent prints on dark-colored surfaces?
- Black carbon powder
- White aluminum powder (Correct answer)
- Gray magnetic powder
- Fluorescent powder
Correct answer: White aluminum powder
White or light-colored powders provide contrast on dark surfaces because the light powder stands out against the dark background.
Question 2: Small particle reagent (SPR) is used on which type of surface?
- Dry porous surfaces like paper
- Wet non-porous surfaces (Correct answer)
- Heated metal objects
- Rough wood
Correct answer: Wet non-porous surfaces
SPR is a suspension of molybdenum disulfide that adheres to fatty residues and is designed for wet or submerged non-porous surfaces.
Question 3: 1,8-Diazafluoren-9-one (DFO) primarily reacts with which component of latent print residue?
- Fatty acids
- Inorganic salts
- Amino acids (Correct answer)
- DNA strands
Correct answer: Amino acids
DFO is an amino-acid-reactive reagent that fluoresces under green light excitation, making it useful on porous surfaces before ninhydrin.
Question 4: Which statement best describes the 'sequential processing' strategy for latent prints?
- Apply all reagents simultaneously for best results
- Use the least destructive to most destructive methods in order (Correct answer)
- Start with the strongest chemical to ensure detection
- Randomize the order to cover all possibilities
Correct answer: Use the least destructive to most destructive methods in order
Sequential processing moves from non-destructive techniques (ALS, photography) through progressively more destructive chemical methods to preserve evidence integrity.
Question 5: What type of light filter should a photographer use when capturing fluorescent latent prints under ALS?
- UV blocking filter
- Barrier (long-pass) filter that blocks the excitation wavelength (Correct answer)
- Polarizing filter to remove glare
- Infrared filter for thermal imaging
Correct answer: Barrier (long-pass) filter that blocks the excitation wavelength
A barrier filter removes the excitation light while passing the longer-wavelength fluorescence emitted by the print, improving contrast in the image.
Question 6: Luminol is primarily used to detect which substance at crime scenes?
- Latent fingerprints containing amino acids
- Trace metal residues from firearms
- Blood that has been diluted or cleaned (Correct answer)
- Gunshot residue particles
Correct answer: Blood that has been diluted or cleaned
Luminol reacts with the iron in hemoglobin and produces chemiluminescence, enabling detection of cleaned or diluted bloodstains.
Question 7: A technician develops a print with ninhydrin on a business card. What color does a positive reaction produce?
- Yellow-brown
- Blue-black
- Ruhemann's purple (Correct answer)
- Bright red
Correct answer: Ruhemann's purple
The ninhydrin-amino acid reaction produces a purple compound known as Ruhemann's purple, which is the classic positive indicator.
CSI Latent Print Processing 3
Which powder is recommended for developing latent prints on dark-colored surfaces?