Forensics For Dummies. Douglas P. Lyle

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СКАЧАТЬ 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, your hair (as well as that of your children and your cat), and fibers from the carpets in your house and car. They could place you at the scene of the crime.

      Of course, you’d have an alibi (I hope) and a legitimate reason why your trace evidence was found at the scene. The thief would not be able to offer a legitimate reason for his trace evidence being at the scene, which means the presence of his prints, hair, and carpet fibers would need an explanation.

       Determining who did what where

      

Placing a suspect at the scene of a crime is one of the basic functions of forensic science. The analysis of fingerprints, blood, DNA, fibers, dirt, plant materials, paint, glass, shoe and tire impressions, and indeed every test done by the crime lab, is performed to create an association between the perpetrator and the crime.

      In many cases, the mere fact that a suspect can be placed at the scene is an indication of guilt. A fingerprint on the faceplate of a cracked bank vault, semen obtained from a rape victim, or paint from the fender of a car involved in a hit-and-run accident connects suspects to crime scenes where they have no innocent reason for being.

Chapter 2

      Getting to Know the Forensics Team

       In This Chapter

      ▶ Checking out the duties of criminalists

      ▶ Looking at forensic science specialties

      ▶ Understanding the medical examiner’s duties

      ▶ Getting to know the forensic investigator

      ▶ Offering expert testimony in court

      TV forensics teams have it good: There’s a specialist for every possible field of study and a fancy piece of equipment for analyzing whatever evidence comes in. Unfortunately, that’s not the case even in larger, more sophisticated jurisdictions, much less in smaller ones where law enforcement officers or a single or very small number of criminalists perform all the required duties.

      More often than not, this is due to funding shortfalls. The truth is that most crime labs are severely underfunded. This fact led author Jan Burke to create the Crime Lab Project (https://crimelabproject.wordpress.com), a site that helps raise public awareness of this national problem.

      Police typically are the first officials to arrive at any crime scene. After they determine the nature and exact location of the criminal act and secure the scene, they call in various forensic specialists to document and gather evidence, and then transport it to the crime lab for further testing. Who shows up to handle these duties depends upon the resources and structure of the jurisdiction.

      

Larger crime labs may have a special crime-scene investigation unit (CSIU) that consists of individuals trained in evidence recognition, collection, and preservation. They are also skilled in performing many of the field tests and screening tests that must be done at a crime scene. Although their exact titles and duties vary from jurisdiction to jurisdiction, these specialists can be divided into two groups. I use the terms criminalists or forensic investigators for those who deal with the physical evidence and coroner’s technicians to refer to those who deal with the body in cases of death.

Gathering the Evidence: The Criminalist at Work

      Criminalist is a relatively new term and one that’s not easy to define. It covers a wide range of abilities, responsibilities, and training. Some, such as serologists and chemists, are scientists, while others, such as fingerprint and firearms examiners, are likely to be ex-police officers who have no true scientific training. Still others are technicians with on-the-job training.

      No matter what their specialty or education, the bottom line is that criminalists work with evidence. That can mean a lot of things, from looking for poisons in blood samples to authenticating written documents, but all of it falls under the banner of criminalist.

      

In spite of what you see on TV and in the movies, criminalists aren’t cops (although, in some cases, they are former police officers). They don’t carry guns, interrogate suspects or witnesses, or make arrests. They don’t treat the injured or deal with a dead body. They collect and analyze evidence. That’s it.

      Common job titles for criminalists include the following:

      ✔ Crime-scene investigator: These are the CSI guys and gals who visit the crime scene to locate, collect, protect, and transport any and all evidence to the crime lab. They document the scene by sketching and photographing it, unless there is a sketch artist or photographer on the scene to take over this duty at their direction.

      ✔ Latent print examiner: These specialists examine fingerprints as well as palm and footprints and compare them with prints obtained from suspects, other crime scenes, or print databases. СКАЧАТЬ