Review Sheet - Impression Evidence

When are fingerprints engraved?

Before birth, during fetal development; they remain unchanged throughout life.

What are friction ridges and what is their purpose?

Raised skin patterns on fingers and palms that provide grip and help identify individuals.

Why are fingerprints good to use for identification purposes?

They are unique, permanent, and can be easily classified.

Who is Bertillon?

Alphonse Bertillon developed the first scientific system of personal identification using body measurements.

What is anthropometry? What happened in 1903 to show that this system isn’t good at individualizing people?

Anthropometry identifies people by body measurements; the Will West case in 1903 showed two men had nearly identical measurements, proving it unreliable.

Contributions of Herschel, Faulds, Galton, Locard, and Henry

Herschel: used fingerprints on documents in India; Faulds: proposed fingerprints for identification; Galton: studied fingerprints scientifically; Locard: created exchange principle, supported fingerprint evidence; Henry: developed classification system still used today.

Fingerprint patterns: loop, whorl, arch, composite, tented arch, double/twinned loop

Loop: enters/exits same side; Whorl: circular pattern; Arch: ridges enter one side, exit other; Composite: combination; Tented arch: sharp rise; Double/twinned loop: two loops intertwined.

How can you tell a radial loop from an ulnar loop?

Radial loops open toward the thumb; ulnar loops open toward the little finger.

What percent of the population has loops? Whorls? Arches?

Loops: ~65%, Whorls: ~30%, Arches: ~5%.

What are minutiae? Be familiar with core, delta/tri-radius, crossing over, bifurcation, island, ridge ending

Minutiae are ridge details used for comparison; examples include core (center), delta (triangular area), crossing over (bridge), bifurcation (split), island (short ridge), ridge ending (termination).

How many ridge characteristics must match before you can say two prints came from the same source?

No fixed number; typically 8–16 matching points are accepted depending on jurisdiction.

How do you determine ridge counts?

Count ridges between the core and delta.

How might fingerprint patterns vary from one person to another (4 ways)?

Pattern type, ridge count, minutiae placement, and overall ridge flow.

What CAN’T fingerprints tell us?

Age, gender, or race of a person.

What is AFIS?

Automated Fingerprint Identification System; a database that compares fingerprints digitally.

How to calculate the primary group using the Henry classification system?

Add values of whorls on even-numbered fingers over odd-numbered fingers, plus 1 to both numerator and denominator.

What is the integumentary system?

The body system including skin, hair, nails, and glands.

What are eccrine glands?

Sweat glands found in skin ridges that secrete water and salts, leaving latent prints.

Define and give examples of Latent, Patent, Plastic prints

Latent: invisible, from sweat/oils (on glass); Patent: visible, from blood or ink; Plastic: impression in soft material (wax, clay).

When should you use fingerprint powder?

On nonporous surfaces to develop latent prints.

What advantage does a Magna Brush have over powder?

Uses magnetic powder, reducing risk of damaging prints.

Describe iodine fuming. What is the iodine reacting with?

Iodine vapors react with oils/fats in prints to produce a temporary brown print.

Describe ninhydrin development. What is it reacting with? What color is the print?

Ninhydrin reacts with amino acids, producing a purple/blue print.

Describe super glue fuming. What color is the print?

Cyanoacrylate vapors react with moisture, forming a white print.

In what order should you use chemicals for latent print development and why?

Iodine → ninhydrin → super glue; use least destructive first to preserve evidence.

What is a tool mark? What cases typically involve tool marks?

Any impression or scratch from a tool; usually seen in burglary or forced entry cases.

Why shouldn’t an investigator ever try to fit a recovered tool into a questioned mark?

It can alter or damage the original evidence.

How might a tool reveal individual characteristics?

Wear, nicks, and scratches create unique markings.

How do you determine tire track width? How do you determine tire tread width?

Track width: distance between left and right tires; tread width: width of the tire pattern contacting the ground.

Wax must be used before making a cast of impressions left where?

In snow or moist surfaces to prevent melting or damage.

Give an example of how an investigator would create a standard for a tool mark.

Use the suspect tool to make test marks in a soft metal for comparison.

Describe two ways to lift evidence in dust.

Electrostatic dust lifter or adhesive lifter.

Give two materials good for making casts. Why isn’t Plaster of Paris used anymore?

Dental stone or silicone; plaster of Paris cracks and gives less detail.

How might lip prints vary from one person to another?

By groove patterns, thickness, and shape.

About what percent of your total height is your foot?

Approximately 15%.