Forensics For Dummies. Douglas P. Lyle
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Police raided the home of one of Capone’s hit men, finding two Thompsons that later were identified as two of the murder weapons.
Identifying common procedures
Scientific services offered by modern crime labs and medical examiners’ offices are varied and complex. The number of services supplied by a particular laboratory depends on its size and budget. State and regional labs may provide a wide array of services, whereas local labs may provide only basic testing. These smaller labs typically outsource more sophisticated testing to larger regional labs. In addition, the FBI’s National Crime Lab offers services to law enforcement throughout the country. Not only does the FBI lab perform virtually every type of test, it also possesses or has access to databases on everything from fingerprints and tire-track impressions to postage stamps.
Larger labs often feature separate departments for each discipline, while smaller labs tend to combine services, perhaps even relying on a single technician to do all the work. Obviously, in this circumstance, a great deal of the work must be sent to larger regional labs.
Common procedures conducted in a crime lab include
✔ Fingerprint analysis (Chapter 5)
✔ Tool-mark and impression analysis (Chapter 7)
✔ Blood analysis (Chapter 14)
✔ DNA analysis (Chapter 15)
✔ Toxicological testing (Chapter 16)
✔ Trace evidence evaluation (Chapter 17)
✔ Firearms examination (Chapter 18)
The first forensic scientist came not from the world of science but from the world of fiction. Sir Arthur Conan Doyle’s character Sherlock Holmes frequently used the sciences of fingerprinting, document examination, and blood analysis to solve the crimes he investigated. In fact, in the first Sherlock Holmes’ novel, A Study in Scarlet, Holmes developed a chemical that determined whether a stain was blood.
Similarly, Mark Twain employed fingerprint evaluation in two of his works (Life on the Mississippi and Pudd’nhead Wilson) nearly a decade before they became recognized investigational tools.
The first real-life forensic scientist was Hans Gross. In 1893, he published the first treatise on the use of scientific knowledge and procedures in criminal investigations. Others soon followed.
In 1901, Karl Landsteiner discovered that human blood could be grouped and devised the ABO blood groups that still are in use today. In 1915, Leone Lattes developed a simple method for determining the ABO group of a dried bloodstain and immediately began using it in criminal investigations. Today, ABO typing, though not able to absolutely identify a particular person, is used to exonerate some suspects, to refute paternity, and to reconstruct crime scenes.
Early in the 20th century, Calvin Goddard perfected a system for comparing bullets under a comparison microscope to determine whether they came from the same weapon. And, Albert Osborn laid down the principles of document examination in his book, Questioned Documents, which still is used today.
Crime-scene investigators are charged with finding, collecting, protecting, and transporting all types of evidence to the crime lab. Although each person or team may have different ways of doing things, typical equipment and supplies they take to the scene include the following:
✔ Crime-scene tape to demarcate and secure the scene
✔ Camera and/or video recorder to document the scene and the evidence
✔ Sketchpad and pens for scene sketches
✔ Disposable protective clothing, masks, and gloves
✔ Flashlight-alternative light sources such as laser, ultraviolet, and infrared lighting for exposing certain types of evidence
✔ Magnifying glass, tweezers, and cotton swabs for collecting hair, fiber, and fluid evidence
✔ Paper and plastic evidence bags and glass tubes to collect and transport evidence
✔ Fingerprint supplies, which include ink, print cards, lifting tape, and various dusting powders and exposing reagents such as luminol
✔ Casting kit for making casts of tires, footwear, and tool-mark impressions
✔ Serology kit for collecting blood and other bodily fluids
✔ Entomology kit for collecting and preserving insect evidence
✔ Hazmat kit for handling hazardous materials
Known as the Locard Exchange Principle, after Dr. Edmond Locard, the French police officer who first noticed it, the exchange of materials is the basis of modern forensic investigation. Using this principle, forensic scientists can determine where a suspect has been by analyzing trace evidence (any small piece of evidence), such as fibers on clothing, hair in a car, or gunk on the soles of shoes.
Looking at Locard’s principle in action
As an example, say that you have two children and a cat. You run out to take care of some errands that include stopping at a furniture store, the laundry, and the house of a friend who has one child and a dog. From a forensic science standpoint, this sequence of events can provide a gold mine of information.
You leave behind a little bit of yourself at each stop, including
✔ Hair from yourself, your children, and your cat
✔ Fibers from your clothing and the carpets and furniture in your home and car
✔ Fingerprints and shoeprints
✔ Dirt and plant matter from your shoes
✔ Biological materials, if you accidentally cut yourself and leave a drop of blood on the floor or sneeze into a tissue and then drop it in a trash can
But that’s not all. You also pick up similar materials everywhere you go:
✔ Fibers from each sofa or chair you sat on at the furniture store ride away on your clothes, as do hair and fibers left behind by customers who sat there before you.
✔ Fibers of all types flow through the air and ventilation system and settle on each customer at the laundry.
✔ Hair from your friend, her child, and her dog latch on to you as do fibers from your friend’s carpet and furniture.
✔ Fibers, hairs, dirt, dust, plant material, and gravel are collected by your shoes and pants everywhere you set foot.
In short, by merely running errands, you become a walking trace evidence factory.
Reading the trace evidence
An examination of your clothes and shoes after the preceding expedition essentially provides a travelogue of your errands. If someone robbed your friend’s house that evening while your friend was away, criminalists would find your fingerprints,