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 can be divided into presumptive and definitive methods. Presumptive identification relies on general traits shared by many individuals (e.g., sex, race) and helps narrow down potential candidates, but is insufficient for establishing a legally binding identification. Definitive identification relies on biological markers that are unique to a single individual (e.g., dactylography, DNA fingerprinting) and confirm the identity of a single individual.

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

Corpus Delicti

The term 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.

• Presumptive identification relies on general traits shared by many individuals, allowing investigators to filter through potential candidates.
• Because these markers are not unique, they are insufficient for establishing a legally binding identification without additional evidence.
• The key characteristics for presumptive identification are:
  • Race
  • Sex
  • Age
  • Stature

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

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

General principles

• Accuracy of sex determination from skeletal remains increases significantly as more components of the skeleton are analyzed together
  • Pelvis: 95%-98% in adults, unreliable in children and fetuses
  • Skull: 80–90%
  • Long bones: 75–90%
  • Pelvis and skull combined: 95–98%
  • Complete skeletal set: up to 100% in ideal conditions
• Conclusions should be based on multiple features, not single traits
• Accuracy can vary depending on population, preservation, and observer experience

Skeletal findings

General characteristics

Skull

Pelvis

Sacrum

Indices

• Sciatic index: higher in females
• Ischiopubic index: higher in females
• Corporobasal index: higher in males

Indicators

Overview

Before age 25, age estimation is typically accurate because the human body follows a predictable development. After age 25, age estimation is less accurate since people 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, which is the most reliable, and ossification are used for age estimation.
• Adult
  • In adults, 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 non-linear, 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 crown-heel length and crown-rump length (CRL)
  • CHL can be estimated from CRL, which is often measured earlier in pregnancy
  • Formula: CHL = CRL x 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
  • Between 6 years and 12 years
  • The total number of teeth remains constant at 24.
• Permanent teeth (32)

Dental charting

• Universal Numbering System
  • Dental identifying system to identify each permanent tooth with a number from 1 to 32
    • Upper jaw, right to left from 1 to 16
    • Lower jaw, left to right 17 to 32
  • Most commonly used in the US
  • Primary teeth are labeled A-T instead of numbers in the same pattern as permanent teeth
• Palmer notation
  • Dental identifying system that assigns teeth with a combination of numbers/letters and quadrant symbols
    • For each quadrant, teeth are numbered 1 to 8
    • Counting starts from the central incisor
  • Primary teeth are labeled A-E instead of numbers
  • Commonly used in the UK and orthodontics
• FDI World Dental Federation notation
  • Dental identifying system that uses a two-digit number for each tooth
    • 1st 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
    • 2nd digt indicates tooth position (from medial to lateral, e.g., central incisor = 1, lateral incisor = 2)
  • Most widely accepted international system
• Haderup notation
  • Dental identifying system that uses number/letters with plus and minus signs to indicate upper/lower jaw and side of the mouth
    • Permanent teeth are numbered 1 to 8 from medial to lateral
    • Primary teeth are numbered 01 to 05
    • A plus sign stands for maxilla, the minus sign stands for mandible
    • 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 since it requires tooth sectioning
  • After scoring, a regression formula is used to estimate the age
  • Formula: Age = 11.43 + 4.56 x (total score)
  • Modifications of this method exist (e.g., Johanson modification) that aim to improve accuracy
  • Reliability decreases from anterior to posterior:
    • Central incisors: most reliable
    • Lateral incisors: moderate reliability
    • Premolars: lower reliability
    • Molars (M₃): least reliable

  ‎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
  • Non-destructive
  • X-ray is used to assess, e.g., secondary dentin formation and reduction in pulp chamber size
• Cementum annulation: microscopic counting of incremental lines in tooth 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

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 in adults. 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.

• Considered the most reliable adult aging method
• In a young person, the surface is rough and billowed.
• As people age, the pubic symphyseal surface smooths out and eventually develops a distinct rim and bony breakdown (Todd method).

Regression formulae

Regression equations (e.g., Trotter & Gleser, Karl Pearson formulas) are a widely utilized statistical method 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 x femur length
      • Female: height = 72.884 + 1.945 x femur length
    • Limitation: developed on specific populations, so adjustments are necessary when the formula is applied to other ethnic groups
• Regression
  • Most accurate method for stature estimation from bones
  • Examples
    • Male: stature = 2.32 x femur length + 65.53
    • Female: stature = 2.47 x 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 illustrate how much each bone/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 (fingerprinting)
  • DNA fingerprinting
  • Anthropometry
  • 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 ∼ 10–12 weeks and are well established by 16–20 weeks IUL. Fingerprints remain unchanged until decomposition.

Primary patterns

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

Core and delta analysis

• Overview: Core and delta 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 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: the study of microscopic features along ridge margins
• Includes:
  • Shape
  • Position
  • Number

Pore structure

• Poroscopy: the study of sweat pore ridges
• Includes:
  • Shape
  • Position
  • Number

Dermatoglyphic abnormalities

• Increased ridge spacing
  • Causes include abnormal connective tissue deposition, edema, and soft tissue overgrowth
  • Examples include: acromegaly, hypothyroidism, congenital lymphedema/chronic edema, rickets
• Irreversible ridge damage
  • Occurs when the stratum basale is destroyed
  • Examples include: thermal injuries (burns, forstbite), 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 include 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: > 5mm
    • 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