Contributor Mimic continues her fascinating, and very informative series of articles on the subject of Forensic sciences. Here is the second part of the next subtopic.
Article by Mimic.
Page editor: XScribe.
While fingerprinting and DNA analysis are probably the most commonly recognized methods used for identifying suspects, there are many weapons in the crime investigator's arsenal, some time-tested and others so new we don't yet know what benefits they might provide in the future.
The Writing on the Wall
Activity time! Everyone get out a piece of paper and a writing implement. Now write something. Anything. Just do it without thinking. Your name. Your address. This sentence. When you're done, study the image you've created on the paper. Notice how you make the letter "e," what shape you use for "g," "y" or "j" tails, how tall your "b," "l" and "t" are. Even if you tried to disguise your handwriting, many of those unique characteristics would be identifiable as yours when compared to another sample of your writing. In forensic science, handwriting analysis when conducted by a questioned documents examiner can be used in this way to provide clues to a particular crime.
Handwriting analysis is based on the assumption that no two people write exactly the same way. The handwriting of most children looks very similar, especially if those children all went to schools in the same general area. Different copybooks are used in different regions for teaching children how to write. But once we grow up, the individual characteristics of our handwriting become uniquely our own. Although the way we form our letters may look very similar to a sibling's or a parent's handwriting, the chances that any other person will have the exact same twenty to thirty specific individual characteristics is pretty close to nil.3 When it comes to validating documents or narrowing down a list of suspects, this is good news for investigators.
Two days after Christmas 1922, a package that was assumed to be a belated gift exploded and killed Clementine Chapman as she tore off the wrapping paper. Her husband, James, was severely wounded. Luckily for investigators in Marshfield, Wisconsin, enough of the wrapping paper survived that they were able to piece together the entire handwritten address. The name of the town was misspelled in such a way that investigators felt the sender was Swedish. It didn't take them long to find the only Swedish resident of the town: John Magnuson, who was known to have a grievance against James Chapman because of a drainage ditch that cut across Magnuson's land. He provided investigators with a handwriting sample, under the mistaken belief that the bomb was totally destroyed. Expert analysis not only connected the pen and ink used to ones owned by Magnuson's daughter, an examination of the handwriting itself found at least fourteen points that matched on both the sample and the reconstructed wrapping. One handwriting expert went so far as to state, "'...by no coincidence could any two persons ever make the characteristic and peculiar repetitions as displayed on these documents.'"1 While Magnuson's attorney spluttered about greedy experts who were only involved for the money, Magnuson's jury found him guilty of murder and sentenced him to life in prison.
Learning to analyze handwriting takes a great deal of training. Most people visualize the job as simply comparing letters written on two sheets of paper, but they must also be knowledgeable about the type of ink, the type of paper, whether it was written by hand or typed, and with the advent of computers/printers, what type of machine was used. Analysis of the letters themselves involves looking at letter form (curves, slants, proportional size between short and tall letters, connecting lines), line form (how smooth the lines are, how dark, how much pressure was used, how fast the person was writing), and formatting (spacing between letters, words, and lines, placement of words on a line, margins).3 But even with all the right training, handwriting analysis is still very subjective. Acceptance by other scientists and as court evidence is not automatic by any means. Hopefully, with increased standardization in training and certification, handwriting analysis will some day be a more powerful tool in the battle to discover "who dun it."
The Better to Bite You With, My Dear
We all heard it as children: "It's not nice to bite people!" Most of us probably stopped and thought about it, imagining how much it would hurt if someone else bit us the same way. But when we're caught in a fight for our lives, teeth often come into play as a weapon. Sometimes they're a part of a killer's bag of kinks, used to create the pain and fear they need to see in a victim in order to obtain satisfaction. Thankfully for forensic odontologists, teeth are one of the most permanent, unchanging parts of our bodies. They are durable and long-lasting-- often the only thing remaining of a person after death--especially in the case of death by fire.1 As such, teeth have been used for both identifying the perpetrator and identifying the victim (we'll talk about the victim aspect in the next article).
Bite mark analysis as perpetrator identification was first accepted into court just over forty years ago. In 1967, it was the main piece of evidence used to convict nineteen-year-old Gordon Hay of the brutal murder of a fifteen-year-old girl. Despite Hay's defense that he was locked in the Biggar, Scotland juvenile detention center, his teeth contained such a unique set of pits and edges that forensic odontologists were able to state that no one else could have left those particular impressions on the victim's breast. In spite of an unsuccessful appeal contesting the admissibility of the marks as evidence, the conviction stood and forensic odontology slowly gained approval with the courts. Indeed, it is often pointed out that Ted Bundy might not have been convicted in 1979 if he hadn't bitten one of his victims at the Chi Omega sorority house. There was no other evidence left behind at the crime scene.
But bite mark identification is a tricky (and controversial) business. If the victim is dead, the marks can change during decomposition. The clarity, location, and type of impression (animal or human) all must be taken into consideration. Many photographs are needed to record the impression, and these days the marks are also tested for DNA evidence, measured extensively, and removed for preservation and silicone casting if the victim is deceased.4 Then the mark is analyzed for any unique features, such as gaps, chips, or jagged edges, that would help to identify the person who left it. But forensic odontology is not an exact science. Cases have come before the courts in recent years where a bite mark misidentification led to a conviction which has since been overturned because of conflicting DNA evidence that was not available during the original trial. Today, bite analysis is considered most reliable under specific conditions, when used to eliminate rather than identify suspects, and when other evidence is available, such as DNA from the bite itself.4
Walk A While in My Shoes
As mentioned previously in these articles, Locard's Exchange Principle tells us that every contact between a person and an object leaves a trace of that person behind. Forensic investigators count on this exchange, especially when it comes to footwear and tire impressions. We've all seen the cop shows with their yellow crime scene tape staked around a patch of field or the shoulder of a roadway. The words on the tape read: “Police line – do not cross." There's a good reason for such a warning at a real crime scene; impression evidence is easily destroyed or altered. If left undisturbed by foot traffic and weather, an impression can last a very long time. But as soon as something else comes in contact with a fresh impression, the shape of it can be irrevocably changed, making it useless to investigators. Hence the need to gather any potential evidence quickly while limiting outside contact.
We don't normally think about the traces our feet leave behind, unless we're tracking mud onto a nice, clean floor. Yet even on a dry surface, where no visible impression is evident, our shoes set up an electrostatic charge for a very short period of time. If fingerprint dusting powder comes in contact with the impression soon enough after it is made, the evidence becomes as visible as a fingerprint.5 Also similar to recording fingerprints, electrostatic impressions can be lifted from floors, tile, and other hard surfaces, but their high degree of vulnerability makes these types of impressions too fragile and short-lived to be useful for many investigations.
Of more use to forensic scientists are the three-dimensional impressions left in malleable surfaces such as mud, sand, snow, or anything else that will hold its shape after being compressed. Whether caused by a sneaker or a vehicle tire, three-dimensional impression evidence is handled pretty much the same way. Lights shining at an angle across the ground illuminate depressions left behind, allowing investigators to cordon off the area and isolate the evidence. As with many other types of evidence, photographs are taken to document the impression's existence. Then a semi-liquid compound, such as the dental casting material used by dentists to make a mold of a patient's teeth, is poured into the indent left by the impression and allowed to harden.5 The finished cast is then pried out of the impression and preserved for study by experts who will compare patterns in the impression to known shoe and tire treads in order to narrow down the maker. If investigators should come up with a suspect at some point in the future, that person's vehicle and footwear can be compared to the casting as well. Individual peculiarities due to wear will be visible in the three-dimensional casting, allowing investigators to see whether or not the suspect's impressions match the ones at the crime scene. More common than fingerprints, impression evidence is part of the ever-growing tool box available to forensic science.
But we're not done yet! Part 3 will look at the forensic wave of the future, as well as one of the most-recognized (and most-often disputed) arm of forensic investigation: psychological profiling.
1 Evans, Colin. The Casebook of Forensic Detection. John Wiley & Sons, NY: 1996. Print.
2 How Stuff Works: Forensic Science
3 How Stuff Works: Handwriting Analysis
4 How Stuff Works: Forensic Dentistry
5 How Stuff Works: Impression Evidence