Forensic human identification

Forensic human identification provides a scientific framework for establishing the legal identity of an individual (whether living, dead, or represented by skeletal remains) through the evaluation of biological and physical markers. Forensic human identification methods may be presumptive or definitive. Presumptive identification relies on general traits shared by many individuals (e.g., sex, race) and helps narrow down potential candidates, but it is insufficient to establish a legally binding identification. Definitive identification relies on biological markers that are unique to a single individual (e.g., dactylography, DNA fingerprinting) and can confirm an individual's identity.

Forensic human identification is the process of confirming a person’s identity (whether living or dead) for legal purposes.

Corpus Delicti

Corpus delicti means "the body of the crime." In forensic medicine and judicial proceedings, it refers to the objective evidence that a crime has been committed. In crimes like homicide, establishing the "identity of the corpus" is a critical piece in evidencing the occurrence of injury or loss.

Identification methods

Identification methods are categorized based on their level of certainty and the biological traits they analyze.

• Uses anthropometric markers shared by many individuals (e.g., race, sex, age, stature) to filter through candidates
• Markers are not unique.
• Insufficient to establish a legally binding identification

Race and sex are the most reliable indicators in building a biological profile from skeletal remains.

Ancestry estimation can be done using multiple skeletal and dental traits. The cranium provides the most informative features, while long bones are less reliable. Identification is probabilistic, not definitive.

Anthropometric indices

• Cephalic index (cranium): numerical value that can be used to describe head shape
  • Formula: (maximum breadth of skull/maximum length of skull) × 100
  • Classification
    • Dolichocephalic (70–74.9): African, Aryan
    • Mesocephalic (75–79.9): European, Chinese, Indian
    • Brachycephalic (80–85): Japanese
• Brachial index: ratio of the radius to the humerus (upper limb)
• Crural index: ratio of the tibia to the femur (lower limb)
• Intermembral index: comparison of the upper and lower limbs

Dental features

• Asian ancestry
  • Shovel-shaped incisors
  • Taurodontism
  • Enamel pearls on premolars
  • Pointed canines
  • Absent 3rd molar
• European ancestry: Carabelli cusp on the maxillary first molar
• African ancestry: increased tooth size and extra cusps

General principles

• Accuracy of sex determination from skeletal remains varies according to bones used.
  • Pelvis: 95–98% in adults
  • Skull: 80–90%
  • Long bones: 75–90%
  • Pelvis and skull combined: 95–98%
  • Complete skeletal set: up to 100% in ideal conditions
• Accuracy increases when multiple components of the skeleton are analyzed.
• Conclusions are based on multiple features, not single traits.
• Accuracy varies depending on population, preservation, and observer experience.

Skeletal findings

Skeletal sex estimation is most reliable after adolescence.

General characteristics

Skull

Pelvis

Sacrum

Indices

• Greater sciatic notch index: higher in female individuals than male individuals
• Ischiopubic index: higher in female individuals than male individuals
• Corporobasal index: higher in male individuals than female individuals

Indicators

Overview

Before 25 years of age, age estimation is typically accurate because the human body follows a predictable development. After 25 years of age, age estimation is less accurate, as individuals age at different rates based on lifestyle and genetics.

• Fetus
  • Crown-heel length is most commonly used to estimate gestational age.
  • Ossification centers can help confirm fetal maturity.
• Prepuberty (childhood): Teeth eruption, teeth mineralization (most reliable), and ossification are used for age estimation.
• Adult
  • Secondary (degenerative) dental changes, cranial suture closure, and pubic symphysis surface change (most reliable) are used for age estimation.
  • Adult age estimations are usually given in ranges (e.g., 35–50 years old).

Crown-heel length (CHL)

• Rule of Haase: a method to estimate the gestational age of a fetus < 5 months of gestation
  • Early fetal growth is nonlinear, which is why a square root relationship is used.
  • Formula: GA = √CHL
• Rule of Morrison: a method to estimate the gestational age of a fetus > 5 months of gestation
  • Fetal growth becomes linear after 5 months, so a direct proportional relationship applies.
  • Formula: GA = CHL/5
• Relation between CHL and crown-rump length (CRL)
  • CHL can be estimated from CRL, which is often measured earlier in pregnancy.
  • Formula: CHL = CRL × 1.5

Dentition

Dentition is the most reliable marker for age estimation in children (mineralization) and remains useful in adults through secondary changes.

Dental development

• Primary teeth: 20
• Mixed dentition period: a period in which individuals have a mix of primary and permanent teeth
  • 6–12 years of age
  • The total number of teeth remains constant at 24.
• Permanent teeth: 32

Dental charting

• FDI World Dental Federation notation
  • Dental identifying system that uses a two-digit number for each tooth
    • The first digit indicates the quadrant and is assigned clockwise.
      • 1–4 for permanent teeth (e.g., upper right = 1, upper left = 2)
      • 5–8 for primary teeth
    • The second digit indicates tooth position (from medial to lateral; e.g., central incisor = 1, lateral incisor = 2).
  • Most widely accepted international system
• Universal Numbering System
  • Dental identifying system to identify each permanent tooth with a number from 1 to 32
    • Upper jaw: right to left, 1–16
    • Lower jaw: left to right, 17–32
  • Primary teeth are labeled A–T in the same pattern as permanent teeth.
  • Most commonly used in the US
• Palmer notation
  • Dental identifying system that assigns teeth with a combination of numbers, letters, and quadrant symbols
    • For each quadrant, teeth are numbered 1–8.
    • Counting starts from the central incisor.
  • Primary teeth are labeled A–E.
  • Commonly used in the UK and orthodontics
• Haderup notation
  • Dental identifying system that uses number and letters with plus and minus signs to indicate upper or lower jaw and side of the mouth
    • Permanent teeth are numbered 1–8 from medial to lateral.
    • Primary teeth are numbered 01–05.
    • Maxilla and mandible are denoted with a plus sign and a minus sign, respectively.
    • The position of the sign indicates the side of the mouth: before the number = right side; after number = left side.
    • Example: +1 = upper right central incisor; -6 = lower right first molar
  • Most commonly used in Denmark and other Scandinavian countries

Secondary dental changes

• Gustafson method
  • Evaluates degenerative changes in six categories, scoring each from 0 to 3
  • Destructive method (requires tooth sectioning)
  • After scoring, a regression formula is used to estimate the age.
  • Formula: age = 11.43 + (4.56 × total score)
  • Modifications of this method (e.g., Johanson modification) aim to improve accuracy.
  • Reliability decreases from anterior to posterior.
    • Central incisors: most reliable
    • Lateral incisors: moderate reliability
    • Premolars: lower reliability
    • Third molars (M₃): least reliable

  Overview of Gustafson criteria
  ‎Parameter	Degenerative change
  Attrition (A)	Wear of the crown increases
  Secondary dentin formation (S)	Pulp chamber size decreases
  Periodontal recession (P)	Loss of alveolar bone; gingival recession
  Cementum apposition (C)	Thickening of cementum
  Root resorption (R)	Resorption of the apical root
  Root transparency (T)	Translucency of dentin increases

• Microscopic evaluation (e.g., of dentin translucency, secondary dentin deposition)
• Radiographic evaluation
  • Nondestructive
  • X-ray: used to assess, e.g., secondary dentin formation and reduction in pulp chamber size
• Cementum annulation: microscopic counting of incremental lines in cementum that is deposited in light and dark annual layers
  • The number of lines corresponds to the number of years that have passed since tooth eruption.
  • Formula: age = cementum lines + eruption age of the tooth
  • Considered a reliable biomarker for age determination in adults when other skeletal indicators are unavailable or unreliable

Ossification

Ossification centers

The timeline of appearance and fusion of ossification centers provides a reliable marker for age from the intrauterine period through early adulthood.

Carpal bones

Closure of skull sutures

Closure of cranial sutures is a supplementary indicator of age. It is based on the progressive fusion of sutures over time, but it is highly variable, limiting precision for forensic age estimation.

Pubic symphyseal surface change

Age estimation using the pubic symphyseal surface is based on predictable, progressive morphological changes of the joint surface with advancing age.

• The most reliable adult aging method
• In early adulthood (approx. late teens to early 20s), the surface is rough and billowed.
• Over time, the pubic symphyseal surface smooths out and eventually develops a distinct rim and bony breakdown.

Regression formulas

Regression equations (e.g., Trotter and Gleser, Karl Pearson formulas) are widely used for calculating height from skeletal measurements.

• Karl Pearson formulas
  • Estimates stature with the help of linear regression calculated from the length of long dry bones
    • Examples
      • Male: height = 81.306 + (1.880 × femur length)
      • Female: height = 72.884 + (1.945 × femur length)
    • Limitation: developed on predominantly European populations and may not apply to all ethnic groups
• Regression
  • Most accurate method for stature estimation from bones
  • Examples
    • Male: stature = (2.32 × femur length) + 65.53
    • Female: stature = (2.47 × femur length) + 54.10

Multiplication factor method

The multiplication factor method is a simplified method where the length of a dry long bone is multiplied by a specific factor to estimate height.

• Femur: 3.6–3.8
• Tibia: 4.5
• Humerus: 5.3
• Ulna: 6.1
• Radius: 6.4–6.5
• Less accurate than regression equations

Percentile of height

Percentiles of height provide an approximation of how much each bone or region contributes to overall stature.

• Femur: 27% (most reliable)
• Spine: 35%
• Tibia: 22%
• Humerus: 20%
• Limitations: vary with sex, population, and body proportion

• Definitive identification relies on biological markers that are unique to a single individual.
• The key methods for definitive identification include:
  • Dactylography
  • DNA fingerprinting
  • Dental identification

Dactylography, or the Galton system, is a definitive method of identification based on the unique and permanent ridges found on the fingertips. Fingerprint ridges begin forming at ∼ 10–12 weeks IUL and are well established by 16–20 weeks IUL. Fingerprints typically remain unchanged until decomposition.

Primary patterns

• Loop (60–70%)
  • Most common pattern
  • Ridges enter and exit from the same side.
• Whorl (25–30%): circular and/or spiral patterns
• Arch (5%)
  • Least common pattern
  • Ridges enter from one side and exit from the opposite side
• Composite: a mixture of patterns

Core and delta analysis

• Overview: Cores and deltas are structural landmarks in fingerprint patterns.
  • Core: the central point of a fingerprint pattern where the ridges show their maximum curvature or turning point
  • Delta: triangular (triradiate) point where three ridges converge or diverge in three different directions
• Analysis
  • Arch: contains 0 cores and 0 deltas
  • Loop: contains 1 core and 1 delta
  • Whorl: contains 1 or more cores and 2 deltas

Fingerprint comparison

For fingerprint comparison, patterns alone are not sufficient, but they are still used for initial classification. For primary identification, ridgeology is the method of choice. Poroscopy and edgeoscopy are high-precision confirmatory methods.

Ridge characteristics (minutiae)

• Ridgeology: the study and comparison of individual ridge characteristics (minutiae)
• Includes:
  • Dots, enclosures
  • Bifurcations
  • Enclosures
  • Ridge endings

Ridge edge details

• Edgeoscopy: a forensic identification technique based on the study of the fine structural details along the edges of friction ridges on the skin
  • Involves the analysis of ridge edge contours, including notches, irregularities, and variations in outline
  • Used to supplement traditional fingerprint analysis, particularly when ridge minutiae are insufficient, or prints are partial or blurred
  • Enhances accuracy in personal identification by providing additional individual-specific characteristics.

Pore structure

Poroscopy is an identification method based on the comparative study of the size, shape, number, and arrangement of sweat pores on the friction ridges of the skin.

• Primarily used in forensic medicine to establish identity when traditional fingerprints are blurred or fragmented
• Analysis includes shape, position, and number.

Dermatoglyphic abnormalities

• Increased ridge spacing
  • Causes include abnormal connective tissue deposition, edema, and soft tissue overgrowth.
  • Examples: acromegaly, hypothyroidism, congenital lymphedema, chronic edema, rickets
• Irreversible ridge damage
  • Occurs when the stratum basale is destroyed
  • Examples: thermal injuries (burns, frostbite), radiation dermatitis, advanced leprosy, scleroderma
• Complete absence: adermatoglyphia
  • Rare condition characterized by complete absence of fingerprint ridges
  • Congenital or acquired
• Atrophy
  • Occurs due to chronic inflammation, loss of dermal support, and thinning of the epidermis
  • Examples: senile atrophy, celiac disease, chronic eczema , psoriasis

• Cheiloscopy
  • Identification based on unique groove patterns (lip prints) using the Suzuki classification
  • Considered supportive evidence that is not as strong as fingerprints
  • Variables like trauma, cosmetics, and inflammation can influence the results.
• Rugoscopy (palatoscopy)
  • Identification based on the unique patterns of the palatal rugae on the anterior hard palate that are unique to each individual, stable over time, and resistant to environmental decomposition
    • Primary rugae: > 5 mm
    • Secondary rugae: 3–5 mm
    • Tertiary rugae: < 3 mm
  • Can be used as supportive forensic evidence (e.g., when dental records or fingerprints are unavailable)
• Podogram
  • Identification based on footprints
  • Particularly useful for identifying newborns in hospital settings
• Bertillon system: an obsolete identification system that uses a combination of anthropometric measurements , descriptive features, photographs, and personal details