Raising Your Standards
Written by Donald J Frost II   

See this article in its original format in the Digital Edition!


Latent print evidence IS one of the most pivotal types of evidence in crime scene investigations. There are classes, seminars, conferences, and publications about the nature of latent prints and about different techniques and tools for their successful recovery and comparison. But at the end of the day, when all the tools and techniques are applied, we should be mindful of the real reason we are recovering those latents. That reason, of course, is so that the latent print evidence can be compared to “something”—and that “something” is known friction ridge print standards. A known friction ridge print standard is kind of the yang to the yin of latent print evidence. Neither really has much value without the other.

A comparison of a “nail-to-nail” rolled impression (left) and a rolled impression (right).

When latent print examiners are working on comparisons, there is usually little thought given to the known friction ridge print standard. The focus tends to be weighted to the latent print, which traditionally is the poorer-quality print being compared. However, when the known print has poor quality, lacking the clarity and detail needed to complete the comparison, we are reminded of the importance of known print standard quality.

Think about how many times you have started working on a comparison of a latent print to a known print and realized that your latent actually has much clearer detail than the known standard. Sometimes the known standard quality is so poor that you can’t even make an ident, having to declare the comparison “inconclusive”. It’s incredibly frustrating; both to the point that it is preventing you from doing your job in solving a crime and also to the point that it probably should almost never happen in the first place. It is true that there are legitimate exceptions to the second point, such as finger, hand, or skin deformities or injuries (or simply an uncooperative person), all of which are influences not in the control of the person obtaining the known print standard. However, many of the poor-quality known prints are simply the result of “operator error”—easily corrected with a little knowledge and effort. This article will discuss some of those factors that are within the control of the person obtaining the known print standard.

The Importance of Print Standards

Known friction ridge print standards may be obtained for a variety of reasons, including but not limited to the booking of arrested persons (typically a full ten-print card and sometimes palm prints or “full case prints”). Known print standards might also be obtained for the summons and release of offenders for less serious charges (a single fingerprint obtained on a specified area of a citation or summons). Also, “non-criminal” known prints might be needed for use as the elimination prints of victims who were in proximity to the crime scene.

Many persons obtaining known print standards (booking officers, street officers, detectives) are unfamiliar with the comparison process and are simply unaware of the importance of high-quality print standards. The assumption is often that if there is some clear ridge detail in some or most of the print or if the digital scanning software accepts the scanned print, then it is sufficient. This mindset can lead to known print standards that have dark blotches or light areas or voids obscuring important print detail. Many of the latents we work with are far from perfect or complete. If a clear, readable area on a latent print has a corresponding poor-quality area on the known print standard (such as the latent print consists solely of a clear delta but the delta on the known print is light, smudged, or missing), completing the comparison can be difficult or even impossible. The more of the known friction ridge print that is clearly captured, the better the chances are that it can be successfully compared to a latent print.

A “perfect” example of a poor fingerprint standard: The ten-print card failed to capture the bottom third of almost every finger on the entire left hand. Most notably, the left ring finger has a whorl pattern, which means it has two deltas below the core. On this ten-print card, the left delta of that finger is missing in both the rolled print and the “slap” print. Unfortunately, in this case, the left delta was the most prominent part of a latent taken from a crime scene. Thus, the examiner was unable to either confirm or eliminate this individual as the source of the latent form the scene.

Utilizing Proper Technique

The first and easiest problem to overcome is simple technique. The person obtaining the known print standard is responsible to work with a cooperative subject in such a manner as to obtain the best possible prints. This involves taking an extra few seconds to explain the process ahead of time and encourage that person to relax and allow the booking officer to do the work. Cooperative subjects may be nervous and unconsciously tense up, making it difficult to manipulate their hands or digits, or they may be overly helpful and attempt to assist by rolling their own fingers or pressing down on the print card, both of which can actually lead to poorer-quality prints. Moderate pressure should be used when obtaining the known print (to prevent the friction ridges from flattening out and touching each other, which can happen under excessive pressure). Fingers should be rolled as close to “nail-bed to nail-bed” as possible (one edge of the fingernail across the dermis at the digital pulp to the opposite edge of the same fingernail). Using one of your fingers from your free hand, apply slight downward pressure on the fingernail of the finger being rolled near the tip of the finger. The additional pressure near the top of the nail bed reduces the common “u” shaped voids that can appear at the top of some fingerprints. For inked plain impression palm prints, the hand should be “rocked backwards” slightly towards the wrist just prior to its removal from the print card to capture ridge detail at the very bottom of the palm where thenar and hyper-thenar meet the wrist. Practicing by printing your co-workers, interns, and police ride-alongs may sound a little silly but can actually be an effective means of improving technique.

Because excessive sweat, dry skin, or soiled hands can affect the quality of a print, a live scan station should be stocked with paper towels (for removing excess moisture) and pre-moistened wipes (for cleaning and adding moisture).

Methods of Capture

Now, let’s look at mechanical factors affecting known print capture. The two most common methods of obtaining known prints for booking purposes are ink (analog) printing and digital scanning (often referred to as “live scan”). Live scan is edging out ink in popularity for booking prisoners, and some agencies may no longer even have the capability or equipment to book arrestees with ink. While the live scan method is arguably easier, faster, and cleaner, some difficult prints can still be captured more effectively with ink (so don’t be so quick to pitch those tubes of ink, ink rollers, and bottles of slab cleaner).

Standard ink printing is typically accomplished in one of two ways: utilizing ink rolled out into a thin film onto a glass or metal platen, or using a portable pre-inked pad. (Portable ink pads are also used as a means of ink capture at the street level for summonses citations.) Another version of ink capture used for elimination prints is commonly referred to as inkless printing. Inkless print kits are available through most vendors and consist of a pre-moistened pad (treated with an invisible fluid) and a stack of ten-print sheets of specially treated paper. The finger is rolled across the pad just like normal ink capture and then rolled onto a specially treated paper ten-print card. The treated paper reacts with the liquid reagent turning black in color where contact is made, mimicking the effects of normal inked printing.

Probably one of the least-known and most under-utilized methods of known analog print capture is latent print capture. Instead of applying ink to the person’s fingers or palms, that person simply provides a latent print impression. Latent print capture, while not advisable for booking prints, can be sufficient for elimination prints and in an emergency for summonses if an ink pad is not available. While known latent prints may not be the best practice for summonses, it can yield a high-quality known print when processed soon after with magnetic fingerprint powder (and is certainly better than acquiring no print at all). Elimination fingerprints and palm prints from victims can be captured by having them rub their forehead and face with their hands and depositing their latent prints on clean printer paper, acetate sheets, or large hinge lifts and processing those prints with fingerprint powder and covering them with lift tape or hinge lift tops. Obtaining their known latent prints allows them to stay clean (no messy ink) and requires fewer supplies be transported to the scene. One simply has to be careful not to overlap the latent prints since they are difficult to see prior to processing.

Fingers should be rolled as close to “nail-bed to nail-bed” as possible (one edge of the fingernail across the dermis at the digital pulp to the opposite edge of the same fingernail).

Quality Control

Regardless of which method of friction ridge print capture is used, there are several factors that affect the friction ridges themselves which can influence the quality of their capture. These factors include moisture content (too little moisture with dry skin or too much moisture with excessive secretion), foreign contaminants, and shallow ridges. They’re easy factors to address, but awareness is the number-one key.

Visually inspect the friction ridge skin before proceeding with any printing technique. Excessive sweat, very dry skin, or soiled hands can impede any of the methods we’ve discussed (but are usually easy to spot and remedy). Having the person simply wash their hands can often help alleviate these issues. Contaminant and secretion removal are obvious benefits of washing hands, but hand washing also introduces moisture to the friction ridges of dry skin, and even after the hands are dried, some moisture is retained for a time. In cases where hand washing is unavailable, the use of moist towelettes or baby wipes can work surprisingly well for cleaning and re-hydrating dry skin. Having the person clutch an article of their clothing or a paper towel between each print rolled can help alleviate excessive secretion.

Sometimes a person being fingerprinted will have very shallow ridges which can make it more difficult to capture good prints. Shallow or worn ridges can also usually be identified during visual inspection. The person being fingerprinted may even volunteer this information (“They usually have trouble getting my prints”). There are commercially available fluids and lotions to help alleviate this problem called ridge-builders. Ridge builders temporarily raise the friction ridges allowing them to more fully contact the fingerprinting mediums.

If you are attempting to obtain known print standards with standard inking, there are a few things you can do to ensure you get the highest possible quality impressions. First, make sure to start with a clean platen and roll out a minimal amount of fresh ink. It’s a temptation to leave ink on the platen from a previous printing and then attempt to freshen it up with additional ink the next time you need to print someone. Applying new ink over the previous ink layer can allow the friction ridges to sink down deeper into the new ink before stopping at the platen, which increases the amount of ink intruding into the valleys of the skin between the friction ridges. Too much ink depth can produce bleed-over inking between the ridges on the ten-print card and obscure ridge detail.

Next, whether you are taking fingerprints or palm prints, obtain a test print on a blank card to see if the ink and the friction ridges will reproduce an acceptable impression. Once you have made any necessary adjustments to the friction ridge skin, and to the fingerprinting equipment and materials, you can proceed with the printing.

These images show three impressions of the same fingerprint under different moisture conditions: (left) Good detail resulted from ideal moisture on the finger; (center) Too much moisture resulted in a very dark impression; (right) Excessive dryness resulted in a very light impression with too little detail.

Fingerprints are often captured in two fashions: rolled impressions and plain impressions (sometimes called “slap prints”). Inked palm prints can also be captured in two fashions as well: a rolled impression on a palm-roller station (a fixed inked drum and a fixed drum card holder for the print card) and then on a flat table as a plain or slap impression (just like the ten-print card). If your agency lacks a palm-roller station for the rolled print, the hands can be inked with the handheld ink roller and any round cylinder of appropriate size can be used as a card holder, such as a large aerosol can or paper towel roll. The plain impressions can be improved by placing a small piece of folded paper towel under the middle of the palm print card. This will cause the middle of the card to push up slightly into the palm, increasing the amount of friction ridge detail recorded at the center of the palm.

If you are attempting to obtain known friction ridge prints with a live scan system, there are a few things you can do to ensure you get the highest quality possible impressions. First, make sure to start with a clean glass platen. A simple spray glass cleaner and soft cloth rag will be all you need to keep the platen clean. You may need to wipe the platen clean of latent print residue between each impression. Keep a roll of paper towels and a container of pre-moistened wipes or towelettes in the work area for moisture control of the skin. The live scan system is extremely sensitive to the moisture in the friction ridge skin. Too little moisture will result in the print being too light and having gaps in the friction ridges. Too much moisture will result in the ridge detail bleeding over (just like with too much ink). Keeping the skin at the proper moisture in a similar manner as the inked printing takes a little effort but is not difficult. Plus, with a live scan system, you can see your print impression before it’s captured.

In lieu of a palm-roller station, a paper towel roll can be used to assist with producing inked palm prints.

Digital Photography for Print Capture

Finally, we should at least mention digital photography as an option. It would likely only be attempted when all other techniques fail. (The technical aspects involved in terms of lighting and post-image production to convert the photographic images to usable known print standards is very much its own animal, and would definitely need to be addressed in detail in a completely separate article.)

Known print standard quality is a subject that actually transcends the forensic community and spans nearly the entirety of law enforcement, so spread the word! Increased efforts will always yield an improved work product. No matter what capacity we serve in law enforcement, whether as a street officer, a case detective, a booking officer, or a print examiner, we have a duty to do our best work at all times. That includes attempting to capture high-quality known print standards. “A prosecutor’s objective is to serve justice so that guilt shall not escape or innocence suffer.” This mantra really applies to all of us who work to bring the case to the prosecutor. We owe it to our community, our agency, and ourselves to put forth our very best effort in such a manner as we would expect from others in our profession if we or our loved ones were ever the victims of a crime. When we do less than our best, we fail justice, we fail our community, we fail our profession, we fail our co-workers, and we fail ourselves. However, when we consistently put forth our best effort, greater success will be our new “standard”.

About the Author

This e-mail address is being protected from spam bots, you need JavaScript enabled to view it is a sworn officer with the Akron (Ohio) Police Department Crime Scene Unit. He is a Master Evidence Technician and has worked as a full time crime scene detective for 14 years. He was a guest instructor with the Ohio Peace Officer Training Academy for eight years and is currently a certified instructor with the Akron Police Department Training Bureau for police academies.

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