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.

Anthropometric indices

• Cephalic index (cranium)
  • Formula: (maximum breadth of skull / maximum length of skull) × 100
    • Classification
      • Dolicocephalic (70–74.9): Africans, Aryans
      • Mesaticephalic (75–79.9): Europeans, 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 (enlarged pulp cavity), enamel pearls on premolars, pointed canines
• Caucasoid: Carabelli’s cusp on the maxillary first molar
• Negroid: increased tooth size and extra cusps

Skeletal findings

Accuracy of sex determination

The accuracy of sex determination from skeletal remains increases significantly as more components of the skeleton are analyzed together.

• Pelvis: 95% (best single indicator, including in children and fetuses)
• Skull: 90–92%
• Long bones: 80%
• Pelvis and skull combined: 98%
• Complete skeletal set: 100%

Age estimation before age 25

• Before age 25, age estimation is typically accurate because the human body follows a predictable development.
• Key indicators
  • Ossification center development
  • Dental development
• Fetal age estimation: primarily based on crown-to-heel length (CHL)
  • CHL = crown-rump length x 1.5
  • Rule of Hasse: < 5 months of gestation, gestational age = √CHL
  • Rule of Morrison: > 5 months of gestation, gestational age = CHL / 5

Ossification center development

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

Carpal bone appearance sequence: Capitate (2 months) → Hamate (3 months to 1 year) → Triquetral (3 years) → Lunate (4 years) → Scaphoid (5 years) → Trapezium/trapezoid (5–6 years) → Pisiform (9–12 years).

Dental development

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

• Primary teeth (20): Eruption begins at 6 months (lower central incisor) and is completed by 24 months.
• Permanent teeth (32): Eruption begins at 6 years (first molar) and is completed by 17–25 years (wisdom tooth).
• Mixed dentition period: Between 6 years and 11 years; the total number of teeth remains constant at 24.

Advanced estimation methods

• Boyde method
  • Counting microscopic incremental lines
  • The neonatal line (appearing at day 2 or 3) is a sign of live birth.
• Stack method: estimates age from the height and weight of the tooth

Age estimation after age 25

• After age 25, age estimation is less accurate since people age at different rates based on lifestyle and genetics.
• Adult age estimations are usually given in ranges (e.g., 35–50 years old)
• Key indicators
  • Cranial suture closure
  • Secondary dental changes
  • Pubic symphyseal surface change

Cranial suture closure

• Coronal suture
  • Upper 1/2: 50 years
  • Lower 1/2: 40 years
• Sagittal suture
  • Anterior 1/3: 40 years
  • Middle 1/3: 50 years
  • Posterior 1/3: 30 years
• Lambdoid suture
  • Lower 1/2: 50 years
  • Upper 1/2: 60 years
• Spheno-occipital suture: 18–22 years

Secondary dental changes

• Gustafson method
  • Evaluates six secondary changes:
    • Attrition
    • Paradentosis
    • Secondary dentin (2nd most reliable)
    • Root resorption
    • Transparency of root (most reliable)
    • Cementum apposition
  • After scoring these six factors, a regression formula is used to estimate the age

Pubic symphyseal surface change

• 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's method).

• Regression formulae: The Karl-Pearson formula is a widely utilized statistical method for calculating height from skeletal measurements.
• Multiplication factor : A simplified method where the length of a dry long bone is multiplied by a specific factor to estimate height.
  • Femur: 3.7 (Best single bone; accounts for ∼27% of height)
  • Tibia: 4.5
  • Humerus: 5.3
  • Ulna: 6.1
  • Radius: 6.5
• Percentile of height
  • Femur: 27% (most reliable)
  • Spine: 35%
  • Tibia: 22%
  • Humerus: 20%

• 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

• Definition
  • Dactylography, or the Galton system, is a definitive method of identification based on the unique and permanent ridges found on the fingertips.
  • These patterns develop between the 12th and 24th weeks of intrauterine life and remain unchanged until decomposition.
• Primary patterns
  • Loop (60–70%): the most common pattern; ridges enter and exit from the same side
  • Whorl (25–30%): ridges form concentric circles
  • Arch (5%): the least common pattern; ridges enter from one side and exit from the opposite side
  • Composite: a mixture of multiple patterns
• Core and delta analysis
  • Loop: contains 1 core and 1 delta
  • Whorl: contains 1 core and 2 deltas
  • Arch: contains 0 cores and 0 deltas

• Advanced identification techniques
  • Ridgeology: the study and comparison of individual ridge characteristics (minutiae)
  • Poroscopy (Locard’s system): the study of the arrangement, size, and frequency of sweat pores along the ridges
  • Edgeoscopy: the study of the microscopic contours and edges of the ridges

• Cheiloscopy: identification based on lip prints (using the Suzuki classification)
• Rugoscopy (palatoscopy): identification based on the unique patterns of the palatal rugae on the anterior hard palate
• Podogram: identification based on footprints; particularly useful for identifying newborns in hospital settings
• Bertillon’s method (anthropometry): an obsolete identification system based on 11 specific body measurements and photographs