Year 10 Forensic Science & Evidence Analysis

Comprehensive practice flashcards covering forensic anthropology, questioned documents and chromatography, ballistics physics and Newton's laws, bloodstain pattern analysis, fingerprinting dactyloscopy, and crime scene investigation protocols.

Who invented anthropometry for human identification, and upon what assumption was it based?

French anthropologist Alphonse Bertillon invented anthropometry in the late 1800s. It was based on the assumption that no two people would ever look exactly alike or have the exact same skeletal measurements.

What mathematical formulas are used in anthropometry to estimate height from femur length?

For males: $\text{predicted height (cm)} = \text{femur length} \times 2.38 + 69.089$. For females: $\text{predicted height (cm)} = \text{femur length} \times 2.317 + 61.412$.

Based on this anatomical comparison, what key skeletal features distinguish a male pelvis from a female pelvis?

A male pelvis is slimmer and taller with a deeper circular (heart-shaped) cavity and a sharper pubic arch ($60^{\circ}-70^{\circ}$). A female pelvis is wider and shorter with a shallower oval cavity and a wider pubic arch ($80^{\circ}-90^{\circ}$) adapted for pregnancy and childbirth.

How can forensic anthropologists differentiate a male skull from a female skull?

Male skulls have a larger brow ridge, a sloping forehead, a square chin, an acute ($90^{\circ}$) jaw angle, and a prominent mastoid process. Female skulls feature a smaller brow ridge, a vertical forehead, a rounded chin, an obtuse jaw angle, and a less pronounced mastoid process.

How do skeletal remains provide evidence for a person's age at death and past medical history?

Age at death is estimated from bone growth stages and wear at joints such as the pubic symphysis and rib ends. Past injuries like healed fractures and surgical repair features (pins and plates) remain for life and can be compared with ante-mortem medical X-rays.

What constitutes a questioned document in forensic investigations?

A questioned document is any written or printed communication whose authenticity or source is uncertain or unknown, such as extortion letters, messages written in blood, questioned passports, licenses, bank records, and counterfeit cash.

In ink chromatography, how do the mobile phase and stationary phase function to separate pigments?

The mobile phase is a liquid solvent (like water or ethanol) that moves up the medium, while the stationary phase is a solid (paper or a thin layer plate) that components adsorb to. Components with higher solubility travel greater distances with the solvent, while less soluble components travel shorter distances.

What is the Retention Factor ($R_f$) in chromatography and how is it calculated?

The retention factor ($R_f$) measures how far a pigment travels relative to the solvent front: $R_f = \frac{\text{distance traveled by the compound}}{\text{distance traveled by the solvent front}}$. It is always a decimal less than $1$, calculated from the origin/baseline to the center of the spot.

What is rifling, and how does it create striation marks on a fired bullet?

Rifling consists of spiral grooves machined inside a gun's barrel that cause the projectile to spin and fly straight. As the bullet travels down the barrel, the metal lands and grooves leave unique micro-scratches called striation marks, individualizing the bullet to that specific firearm.

What forensic comparison technique is depicted here to match a fired bullet to a suspected firearm?

A comparison microscope is used to align striation marks on a crime scene bullet with a test-fired bullet side-by-side. A matching pattern of striations provides physical evidence that both bullets were fired from the same rifled gun barrel.

What forensic information can be derived from gunpowder and cordite burn marks around a gunshot wound?

Gunpowder and cordite residue leave distinct burn marks on a victim's skin that can establish the proximity or distance between the muzzle of the firearm and the victim during shooting.

How do Newton's Three Laws of Motion apply to ballistics?

Newton's 1st Law (Inertia) states a bullet remains at rest until expanding gases apply an unbalanced force, and stays in flight until acted on by gravity and air resistance. Newton's 2nd Law ($F = ma$) relates bullet acceleration to applied propellant force. Newton's 3rd Law dictates that the forward force accelerating the bullet generates an equal and opposite force felt as recoil.

What is the primary scientific difference between speed and velocity?

Speed is a scalar quantity measuring only the magnitude of distance covered over time ($s = \frac{d}{t}$). Velocity is a vector quantity that specifies both the magnitude of the rate of change of position and the direction of motion ($v = \frac{x}{t}$).

What is the average acceleration of a bullet that takes $1.2\,\text{s}$ to slow down from $300\,\text{m/s}$ to $0\,\text{m/s}$?

Using $a = \frac{v - u}{t}$: $a = \frac{0\,\text{m/s} - 300\,\text{m/s}}{1.2\,\text{s}} = -250\,\text{m/s}^2$. The bullet experiences a deceleration of $250\,\text{m/s}^2$.

How much force is required to accelerate a $1400\,\text{kg}$ car at $2\,\text{m/s}^2$?

Using Newton's Second Law ($F = m \times a$): $F = 1400\,\text{kg} \times 2\,\text{m/s}^2 = 2800\,\text{N}$.

On a distance vs. time graph, what do a horizontal flat section and a steep straight line represent?

A horizontal flat line represents a stationary period where no distance is covered ($\text{speed} = 0\,\text{km/h}$). A steep straight line represents steady, constant movement at high speed.

What foundational premise governs bloodstain pattern analysis, and what are its three primary categories?

Bloodstain pattern analysis is based on the premise that all bloodstains and patterns are characteristic of the forces that created them. The three primary categories are passive bloodstains, transfer bloodstains, and projected bloodstains.

According to bloodstain pattern analysis, how does drop height influence the diameter of a passive blood drop?

As the drop height increases, the velocity of the falling blood drop increases due to gravity, causing the resulting bloodstain diameter to increase upon impact.

What is a swipe bloodstain pattern, and how is its direction of travel determined?

A swipe is a transfer bloodstain produced when blood from a moving bloody source is deposited onto an unstained surface (e.g., a bloody hand dragging on a wall). The direction of motion is indicated by its feathered edge.

How are low, medium, and high velocity impact spatters differentiated in projected bloodstains?

Low Velocity Impact Spatter (LVIS) is caused by low-velocity forces. Medium Velocity Impact Spatter (MVIS) is caused by medium-velocity forces, typically beating or bludgeoning trauma. High Velocity Impact Spatter (HVIS) is fine misting caused by high-velocity energy, such as gunshots or high-speed machinery.

How does the angle of impact affect the physical geometry of an impacting blood droplet?

A blood drop falling perpendicularly at a $90^{\circ}$ angle creates a circular stain. As the impact angle decreases and becomes more acute, the drop elongates, forming an elliptical shape with a tail pointing in the direction of travel.

What are cast-off, arterial spurting, and expiratory bloodstain patterns?

Cast-off patterns are created when blood is slung from a moving weapon between blows. Arterial spurting occurs when blood escapes under pressure from a severed artery. Expiratory bloodstains are propelled from the mouth, nose, or lungs by respiratory airflow.

What is the biological function of friction ridges, and when do human fingerprints form?

Friction ridges function like tread on a tire to increase friction and improve grip. They begin forming in the skin between the epidermis and dermis around the 8th week of gestation and are fully developed by the 17th week, remaining permanent throughout life.

What distinguishing characteristics separate latent, patent, and plastic fingerprints?

Latent prints are invisible deposits of sweat, oils, and skin cells that require physical or chemical visualization. Patent prints are readily visible prints left in colored substances like blood, ink, or paint. Plastic prints are 3D impressions pressed into soft media like clay or putty.

What are the four primary pattern classifications in fingerprint identification?

The four main fingerprint ridge patterns are loops (ridges enter and recurve out the same side), arches (ridges flow in wave-like formations across the finger), whorls (ridges form circular or spiral patterns), and composites (combinations of two or more patterns, such as a double loop).

What are bifurcations, ridge endings, and deltas in dactyloscopy?

A bifurcation is a minutiae ridge point that splits into two separate branches; a ridge ending is the point where a friction ridge terminates; and a delta is a triangular ridge divergence located near a loop or whorl pattern.

Which visualization techniques are appropriate for latent fingerprints on porous versus non-porous surfaces?

Non-porous surfaces (glass, polished metal) are dusted with black carbon powder, white aluminium powder, or fluorescent powders, or fumed with superglue (cyanoacrylate). Porous surfaces (paper, cardboard, cloth) are treated with chemicals like ninhydrin (turns purple reacting with amino acids) or iodine fuming.

How does a fingerprint examiner confirm a positive identification between a latent crime scene print and a known print?

An examiner compares friction ridge characteristics (minutiae points like cores, deltas, islands, and bifurcations) between the latent print and a known ten-print card. Identification is established when an adequate number of corresponding points match identically in relative spatial position.

What is the historical and linguistic origin of the term 'forensic'?

The term forensic comes from the Latin 'forensis', meaning 'of or before the forum.' In ancient Rome, criminal charges were debated publicly in the forum, where the individual presenting the most compelling speech and argument won the case.

Who was Edmond Locard, and what fundamental principle of forensic science did he establish?

Edmond Locard (1877–1966), known as 'The French Sherlock Holmes,' founded the first police laboratory in Lyon in 1910. He established Locard's Exchange Principle: 'Every contact leaves a trace'—whenever a person enters an environment or interacts with another, they leave something behind and take something away.

What are the '7 S's' of crime scene investigation in correct protocol order?

1. Securing the Scene
2. Separating the Witnesses
3. Scanning the Scene
4. Seeing (Photographing) the Scene
5. Sketching the Scene
6. Searching for Evidence
7. Securing and Collecting the Evidence

How do testimonial evidence, physical evidence, and trace evidence differ in forensic investigations?

Testimonial evidence consists of oral or written statements presented by witnesses in interviews or in court. Physical evidence refers to tangible objects recovered from a scene or suspect (weapons, tools, documents). Trace evidence refers to microscopic or tiny physical materials found in measurable amounts, such as hairs, fibers, glass, and gunshot residue.

What biological indicators are evaluated by a forensic pathologist to estimate the post-mortem interval (PMI)?

A forensic pathologist evaluates body cooling (algor mortis), body stiffening (rigor mortis), skin lividity and discoloration (livor mortis), the extent of tissue decomposition, and forensic entomology (the life-cycle stages of infesting insects like flies, maggots, and beetles).