While the capture of the Night Stalker was a credit to law enforcement’s use of the media, his identification as Ramirez was the result of another modern technique. The Night Stalker case was among the first major cases to use automated fingerprinting technology.

Today, television detectives run fingerprints from a crime scene through an automated database and get results in seconds—somewhat inaccurately. In reality, the database kicks back “likely” matches and a trained fingerprint examiner must compare them to find an actual match. Still, the technology we use today allows quick searches of a vast number of fingerprints, and if a criminal leaves a fingerprint behind we can see if he’s ever been booked and fingerprinted, or if we have the same print on file from another scene.

In 1985, this use of computers was brand new. Before automated systems, examiners would have to look through fingerprints on file by hand, using ten-print cards (on which a booked criminal has rolled all ten fingerprints in ink). It meant a great deal of time and effort, and was rarely useful without a suspect in mind. Some even admitted that the collection of fingerprints at the scene was frequently done for public relations purposes only—to appear to be doing something to solve the crime.

When computers were first applied to the task, the systems were extremely expensive, making it difficult to sell to agencies with low budgets. That’s why when the California Department of Justice used their brand new automated fingerprint indexing system to immediately identify Richard Ramirez as the Night Stalker, it put these systems on the map—it proved they worked, and that the cost was justified.

For a contemporary article on the use of automated fingerprint technology, go here. For more on the Night Stalker’s crimes, go here.

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The system worked quite well, until 1903 when Will West was received at Leavenworth Penitentiary. Upon running Will West’s measurements, it was discovered that a “William West” was already imprisoned at Leavenworth.  He had the same anthropometric measurements as Will West.  A photographic comparison of the two men did little to distinguish them.   Finally, two years after Will West was brought to Leavenworth, fingerprints of each man were taken, compared, and found to bear no resemblance.  Thus each man was distinguished by his fingerprints.  Needless to say, Leavenworth converted from the Bertillon system to the more reliable fingerprint system, which is still in use today. This is a reminder that fingerprints are important.

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Both New York and Maryland have computerized ballistic fingerprint databases, both states have legal mandates that require all firearms manufacturers to provide, a spent cartridge and prepare ballistics images of the bullets and cartridge casings and provide the records so that the state’s law-enforcement agencies can access it, for every firearm legally sold; the law also requires that the name, address and Social Security number of the person purchasing the firearm be linked to the ballistics information.

The law, and the database, is based on the theory that that every gun marks shells and bullets in specific, stable, identifiable ways.  The reason casings are used is because firearm that produce marks on cartridge cases are less subject to long-term wear.  This theory, unfortunately, has not been scientifically proven.  In fact, the markings left by a gun on a casing are not guaranteed to be the same over the long term and can be deliberately changed with simple tools such as a file or metal brush.

Another problem with the ballistic fingerprint database, as it stands, is that only new gun purchases are beholden to the law, meaning that the millions of already purchased guns cannot be traced via the database.  Other concerns include the fact that less than 1% of legally guns sold will ever be used in a crime, guaranteeing wasted effort.  Beyond that, nearly 90% of guns used in crimes change hands at least once after their initial purchase at a licensed dealer before being used in crimes; it has been estimated that nearly 40% of guns used by criminals are either stolen from their rightful owners or purchased on the black market.

There is also fault with the potential usefulness of such a database.  California did some extensive testing to assess the accuracy of such a database and they found that when shell casings used with a particular gun came from the same manufacturer the computer failed to match the correct casing to its gun 38% of the time; when casings came from different manufacturers the failure rate was 62%.  These false matches waste the time of ballistic examiners who are left ruling out matches made by the computer database. New York has had its database up and running since 2002 and has since entered data from over 200,000 new gun purchases and has spent approximately $1,000,000 a year on its system. By 2007 the system had not led to a single solved crime.

Fingerprint and DNA databases see their success from the fact that neither identifier is subject to change, a person is stuck with the DNA and fingerprints they are born with, but this is not the same for a gun and its parts. The parts of the gun that are responsible for marking a shell casing are the breech face, extractor, ejector, and firing pin, all of which can be purposefully altered with specific tools or all of which may change with time and normal wear.  Although the idea of a ballistic database is appealing given the large amount of gun violence in the US, unfortunately the ease with which guns can be altered appears to throw a monkey wrench in the idea.

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Is bacteria the new forensic tool

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For the process for super glue fuming to occur, the cyanoacrylate must be boiled to achieve its gaseous form.  Once in a gaseous state, the fumes will slowly circulate in the chamber and will engulf the room.  If any latent fingerprints exist on the object being fumed those prints will be exposed to the gaseous cyanoacrylate triggering a chemical reaction. The reaction can take from 5 minutes to over two hours with the exact time determined by the size of the chamber as well as the concentration of the gaseous cyanoacrylate in the air and the humidity of the environment. Care must be taken with cyanoacrylate fuming because when latent prints are exposed to the super glue fumes for too long they can over develop and lose essential detail.

After the fingerprints are developed using the super glue fuming method they can generally last for years; cyanoacrylate fuming can be used to preserve fingerprints since the glue fumes coat latent prints with a hard surface making them harder to accidentally alter or destroy.  Cyanoacrylate fuming also does not preclude DNA testing on items that have been exposed to the fuming process, any blood that has been exposed to cyanoacrylate fumes can still be successfully tested for a DNA profile.  Another positive aspect of super glue fuming is that it is not expensive, the only things required for cyanoacrylate fuming are a bottle of super glue, a heat source, and a chamber to enclose the fumes; many departments use plastic bags as chambers when fuming at a crime scene.

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Fingerprint residue contains natural salt secretions that corrode metals at the points where the salt contacts the metal. This microscopic fingerprint corrosion leaves a permanent mark on metal that cannot be washed away. The heat of the firing of the gun also does not alter these marks.

The new technique that has been established to visualize these types of prints relies on running electrical current over the metal object , such as a bullet casing or a gun, that has been coated with a fine toner like powder. When a charge is run down the metal object the fine conducting powder is attracted to these areas of corrosion revealing a powdered fingerprint.

This technology can also be used in fires to recover prints of metals exposed to very high temperatures.

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• Fingerprint science “does not guarantee that two analysts following it will obtain the same results”.
• Shoeprint and tire-print matching methods lack statistical backing, making it “impossible to assess”.
• Hair analyses show “no scientific support for the use of hair comparisons for individualization in the absence of (DNA).”
• Bullet match reviews show “scientific knowledge base for tool mark and firearms analysis is fairly limited.”
• Bite-mark matches display “no scientific studies to support (their) assessment, and no large population studies have been conducted.”

The art of fingerprint comparisons

There is no denying that a fingerprint examination is a subjective process. When an examiner conducts a common source determination, he or she will compare points of individuality in the two prints and evaluate if their is sufficient quantity and quality of detail in agreement between the unknown and the known prints to reach a conclusion. These assessments are largely based on the examiner’s interpretation of the evidence, and there are no specific measurements or standard tests to benchmark against, except for counting the number of points in agreement. In the U.S., the courts deliberately eliminated a threshold standard of agreement, so that the determination can remain a subjective matter, taking into account the examiner’s training and experience, and both the quantity and quality of comparable details. That is to say that an examiner does not have to observe a minimum number of points in agreement between the unknown and the known print to reach a common source conclusion, but can rely of his or her specific training and experience to guide the examiner to the right conclusion.

As you may have gathered, an element of a fingerprint comparison is dependent on the person doing the examination. An examiner needs to be able to see the fingerprint in a specific way, store that in his or her memory, and then recall it when comparing it to another fingerprint. A person’s ability to recognize shapes, small details, and other spatial relationships is crucial to the job of a fingerprint examiner, and can be considered an art form. It is a learned skill, requiring practice and concentration, and one that is ultimately susceptible to variation.

So, if fingerprint examination is an art, where is the science?

The science of fingerprint comparisons

Fingerprint examinations are deeply rooted in scientific principles. The whole fingerprint field is based on the recognition that no two people will ever have the same fingerprints, and that an individual’s fingerprints will remain unchanged throughout life. Based on these premises, the science of fingerprint comparisons is one that should, in theory, have no error. Either a fingerprint found at a crime scene is the same as the known print or it is not – there is no in-between. The examiner’s methodology is also based on the scientific method. An examiner follows the ACE-V methodology for fingerprint comparisons, which is an acronym for the stages of the examination. Analysis is the first step, where the examiner will look at the unknown print and determine if there is sufficient quantity and quality of friction ridge detail to be able to conduct an examination. Next comes the comparison, where the examiner will look for class and individual characteristics in the unknown fingerprint and compare them with the known prints. In the third stage, the examiner will evaluate the comparison, determine how much weight to attribute to the different similarities and dissimilarities between the prints, and reach a conclusion. The conclusion an examiner can reach is either exclusion (the prints came from different sources), individualization (the prints came from a common source), or no conclusion (there is insufficient amount of information to be able to reach a conclusion). The final stage is the verification stage, where a second examiner will conduct an independent examination on the same evidence and verify the first conclusion. Technically speaking, the examiners should reach the same conclusion since the science behind the examination should lead them to the same results. In this way, fingerprint comparisons should be reproducible and accurate because they are founded on scientific principles.

Understanding the argument

So, why does the report state that fingerprint science “does not guarantee that two analysts following it will obtain the same results”? Well, because essentially it does not. The emphasis on that statement is on the word “guarantee”. Whenever humans are involved in anything, there is the chance for error, even though in theory there should not be any for fingerprint science.  The tone of the statement indicates that each time an examiner conducts an examination on the same evidence there is an equal chance that they will each reach a completely different conclusion, but the science dictates that they should reach the same conclusion every time. Should that discredit fingerprint science? Some people believe that it should, especially since the error rate for fingerprint science has not been uncovered. The scientific community goes through great lengths to try to eliminate human error, by instituting random proficiency testing, continuing education, and board certifications as some of the measures to reveal the human error rate and to prevent unqualified individuals from becoming experts in the field. But as we have previously discussed, there is a human element to fingerprint science that even the courts have promoted as being crucial to allowing fingerprint examiners to do their job effectively. In fact, there are automated forms of fingerprint comparisons, such as AFIS (Automated Fingerprint Identification System), which is used to scan databases for a fingerprint match; however, the computers are not “authorized” to conduct an examination en lieu of humans, since the computers can not go to court and testify as to the reliability of their examinations. The U.S. has still mandated that a fingerprint comparison must be done by a person, since that is the most reliable way of ensuring that it is done properly. Computers can not deal with variation like humans can and they can not explain differences that are present in fingerprints from the same person. These philosophies dictate that a system that is too rigid is actually detrimental to fingerprint science, since it restricts the degree to which a person’s training and experience can contribute to a fingerprint comparison.

That leaves us with a “Catch 22”. On the one hand, humans are seceptible to error, even if measures are taken to eliminate those errors. On the other hand, computers, which do not make errors, are not qualified to do fingerprint comparisons. So, we are left with a situation that demands perfection from imperfect beings. While that does not justify the fact that errors occur, it should help us understand why they may occur and it should be a force driving us to reach perfection in our profession. I agree with the report’s call for more research in the human error rate, proficiency testing, advanced training, and stringent certification of examiners and labs, but let’s take the argument into context and understand how it can effectively be applied.

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