Fingerprint comparisons require close observation of fine details. Two samples, whether known prints from a suspect or latent prints from a crime scene, are examined to determine if they were produced by the same individual. An identification, or "ident" is made when the examiner determines there are enough matching points or structures to eliminate all others as producing the print. Based on historical data, two prints bearing six characteristics of the same type in the same relative position are sufficient to ensure identity. In the United States and many other countries, there is no minimum number of points required. It is based on the training and experience of the examiner and their ability to defend their conclusion in a court of law.
The ACE-V method was introduced to standardize the process of fingerprint examination into a more scientific analysis with organized steps and processes following models of the scientific method. The acronym ACE-V stands for Analysis, Comparison, Evaluation, and Verification and each are detailed below.
Analysis – the qualitative and quantitative assessment of Level 1, 2, and 3 details to determine their proportion, interrelationship and value to individualize.
Comparison – to examine the attributes observed during analysis in order to determine agreement or discrepancies between two friction ridge impressions.
Evaluation – the cyclical procedure of comparison between two friction ridge impressions to effect a decision, i.e., made by the same friction skin, not made by the same friction skin, or insufficient detail to form a conclusive decision.
Verification – an independent analysis, comparison and evaluation by a second qualified examiner of the friction ridge impressions.
Fingerprint Comparison Vocabulary
ACE-V fingerprint identification method using analysis, comparison, evaluation, and verification
Bracelet formation of interlaced creases found at the wrist to palm and thumb base to palm junctions
Distal Transverse Crease Top crease running from outside edge of palm to just below base of index and middle fingers
Flexion Crease A crease formed along the folds of the friction skin
Hypothenar Largest portion of uninterrupted palm located on the lower half of the ulnar side of the hand
Interdigital Region of the palm just below the base of the fingers above the distal transverse crease
Misidentification An fingerprint improperly identified as to the source
Proximal Transverse Crease Middle crease running from thumb web to middle area of hypothenar
Radial Longitudinal Crease bottom crease running from thumb web to central base of the palm. Also referred to as the “Life line” by palmists.
Tension Crease Small creases formed due to stretching of the friction skin. Normally form in alignment with the direction of the stress.
Thenar Region of the palm at the base of the thumb
Vestige A section of friction skin in the web area which does not conform to regular flow patterns. It may contain squared loop pairs or perpendicular ridge flow.