Forensic Science HQ

Investigate the forensic science world

Questioned Documents

A forensic scientist specializing in questioned documents usually work cases involving alleged forgery, blackmail, kidnapping and death threats.

Although questioned documents examiners are often referred to in the media as “handwriting experts”, they frequently examine evidence with no hand writing at all.  These items may include printed materials, typewritten documents, photographs, and duplicated productions (copies).   It is often the task of the document examiner to determine if the item in question has been altered, forged, or obliterated.  This requires the use of special light techniques, most commonly infrared or ultraviolet light.  Inks and printing appear differently under certain light depending on their chemical composition and the amount of force applied to the medium.  It is therefore possible to determine if more than one utensil has been used to produce a document and if more than one technique or source has been used.

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For example, a common tactic among forgers is to alter a legitimate check and increase the amount of the draft.  A check for $100 may appear to have changed to read $10,000.  By examining the check under alternate light sources, it can sometimes become very obvious that a two different pens were used to add the additional zeros to the amount.  This type of analysis is photographed and can easily be demonstrated to a jury should the case go to trial.

In the case of handwriting analysis, it is possible to prove that a specific individual did or did not write the document in question.   This is done by obtaining “known” samples of handwriting from the person of interest and comparing those samples to the piece of evidence.   The examiner will look at individual strokes, loops, spacing , and slant.   Determining that someone is NOT the source of a document is often times easier and quicker than concluding that an individual is the source.  In addition to using alternate light sources in their analysis, the question document examiner will also often use various microscopes, including comparison scopes and even electron microscopes.

In addition to handwriting and printed materials, the document examiner may also be asked to perform impression analysis.  This may include evidence involving rubber stamps, gloves, footwear and tire impressions,  indented writing and tool marks, glove impressions, and footwear and tire impressions.
Training to become a question document examiner takes several months and involves case studies and laboratory exercises.   The forensic document examiner must frequently work in close conjunction with latent print examiners, as there is often times a need for fingerprint analysis on the evidence as well as document analysis.

forensic document

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Individuals interested in a career as a document expert should expect slow, methodical work and must be able to explain their analysis to a jury that often confuses the science behind this type of work with the erroneous perception that is a subjective art.   Forensic Questioned Document examiners are not the same as handwriting hobbyists who assign personality traits to various writing styles or to profiling experts who analyze the content and psychological meanings of criminal evidence.

Forensic document examiners in a criminal laboratory determine if a piece of evidence has been altered, obliterated, forged, or otherwise tampered with and who may or may not be responsible for the document based on careful comparison between it and known samples.

Famous cases in the United States that involved question document analysis include the “Unibomber”, the “Zodiac Killer”, and the Jonbonet Ramsey homicide.


Forensic Toxicology

Forensic toxicology is the use of scientific techniques to aid medical or legal investigation of death, poisoning, and drug use.

Forensic Toxicology

Forensic Toxicology

A Forensic Toxicologist may use a variety of analytical instrumentation and techniques to isolate and detect intoxicating substances in various kinds of biological samples.
Isolating the toxic substance from the sample is often the most difficult, as forensic tissues are often old, contaminated or degraded. The sample has to be concentrated and purified as much as possible before being analyzed for identification.

Because many poisons are changed by human metabolism after ingestion, it is important for the forensic toxicologists to gather as much background information from the investigating agency as possible. This information will be used to consider all possibilities of a toxilogical source when presented the data from the analytical results of testing.

The most common types of samples the forensic toxicologists works includes blood, hair, saliva, urine, eye tissue and skin. They may be asked to examine the samples for organic compounds, metals or drugs and present their finding in court as an expert witness.

Latent Prints

“Latent prints” is a term used to describe the forensic discipline of identifying fingerprints, palm prints, toe and sometimes even lip prints to a single individual. The term “latent” actually means hidden, which of course, fingerprints at a crime scene usually are. Forensic scientist also examine “patent” prints, which means obvious, or clear , i.e. not hidden. An example of a patent print may be one made in blood and easily visible.

Fingerprint examination has been in use as an identification technique for over a hundred years.

Human fingers have friction ridges in the skin which makes up a unique pattern. No two people, and in fact, no two fingers have the same pattern. Therefore, matching a fingerprint to the finger that it originated from is an absolute identity.

latent print

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A fingerprint is made when the debris from the friction ridge of the skin comes in contact with an object. The debris is usually dirt, oil, perspiration, grease or ink. The print is often “lifted” from the surface, which simply means transferred to something that can be moved. It is then brought to the lab and the forensic scientist may use a vast array of procedures, such as the application of powders, chemicals, fumes and dyes to make it visible. Special devices, including powerful ultraviolet lamps and lasers, may also be utilized.

Once it can be seen, the print is photographed, scanned and examined. The Latent Print examiner spends tedious hours studying the patterns of the print, and identifying specific points of the ridge pattern that make it unique. If enough detail can be found through the analysis, the pattern can be compared to known prints of suspects and victims. People are then included or eliminated as a possible source of the print. Many times, upon completion of their analysis, the latent print examiner is able to positively identify or exclude a person of interest. A positive identity is the most powerful form of forensic analysis and therefore the most sought after in the legal system.

Latent prints may also be searched against a nationwide database of prints known as AFIS (Automated Fingerprint Identification System). AFIS contains the fingerprints of millions of persons, as well as unknown prints of other crime scenes. The computer analysis will provide a list of possible matches to the forensic scientist who will then manually compare the results to determine if a complete match really exists. Thousands of cases are solved or linked together as a result of the AFIS system every year.