The ACE-V method explained

What is a latent print?

The skin on your fingertips carries raised lines called friction ridges. When a finger touches a surface, sweat and natural oils on those ridges can leave a copy of their pattern behind. Many of these marks cannot be seen with the naked eye, which is why they are called latent prints. They are made visible with powders, chemicals or lighting suited to the surface, and photographed before anything else is done.

Latent prints are often partial, smudged or laid over one another. Nobody presses a finger down neatly on a door handle or a sheet of paper. Known prints are different: they are taken deliberately from a named person, under controlled conditions, so that every finger is recorded clearly. ACE-V is the discipline that connects the two.

The four stages of ACE-V

1. 01

   Analysis

   The examiner studies the latent print on its own, before looking at any known print. They note the overall ridge flow, individual features such as ridge endings and bifurcations (points where one ridge splits into two), the clarity of the mark and any distortion caused by pressure or movement. They then decide whether the mark holds enough reliable detail to be compared at all.

2. 02

   Comparison

   The latent print is set side by side with the known prints. The examiner checks whether the same features appear in the same places and in the same relationship to one another, working from the latent mark towards the known print rather than the other way round.

3. 03

   Evaluation

   The examiner weighs the agreements and any differences, asking whether a difference can be explained by distortion or is genuine. The outcome is one of three: the marks share a source, they do not, or there is not enough detail to decide.

4. 04

   Verification

   A second qualified examiner looks at the same material and reaches their own conclusion. If the two disagree, the difference is discussed, resolved and recorded rather than set aside.

Why does a second examiner matter?

Fingerprint comparison depends on trained human judgement. Like any judgement, it can be affected by tiredness, a poor-quality mark or knowing too much about the wider case. An independent second look catches mistakes before a report goes out, and means the conclusion does not rest on one person’s view alone.

Findings are peer-reviewed by a senior examiner in line with our standard operating procedures. Each comparison is then reported with a signed certificate.

Context can sway any examiner. Good practice keeps attention on the ridge detail itself and shares only the case information the examination actually needs.

What a fingerprint report can and cannot say

A fingerprint report can:

• state whether each latent print is suitable for comparison;
• give the conclusion reached for each latent print against each set of known prints;
• show the ridge features relied on, usually on marked-up enlargements;
• record how the exhibit was received and how the mark was developed and photographed.

It cannot:

• tell you, in most cases, when the print was left;
• explain how or why the person came to touch the surface;
• say anything about someone whose known prints were not supplied;
• turn a weak mark into a firm answer. An inconclusive result is an honest outcome, not a failure.

Where a report is used in proceedings, it is evidence for the court to weigh with everything else. Whether evidence is admitted is decided by the court in each case.

Before you send an exhibit

• Handle the item as little as possible, by its edges, ideally wearing clean gloves.
• Do not dust or treat it yourself. A failed attempt can destroy the mark for good.
• Pack dry items in a clean paper envelope or box rather than plastic, which can trap moisture.
• Note who found the item, where and when, and everyone who has handled it since.
• Think about elimination prints: known prints from people with an innocent reason to have touched the item, so their marks can be ruled out.

Terms in this guide

• ACE-V
• Latent print

Questions