Forensics For Dummies. Douglas P. LyleЧитать онлайн книгу.

Obtaining a search warrant

▶ Gathering and preserving evidence

▶ Figuring out where the body went

Crime scenes are like puzzles and, when investigators are lucky, the pieces fit neatly together. In other cases, determining what happened is like trying to create a picture from two or three different puzzles where you have plenty of pieces, but they don’t fit. And investigators often have to deal with pieces that just aren’t there.

Because solving a crime and convicting a perpetrator depend upon evidence, investigators take a methodical approach to finding and handling evidence at crime scenes. They work hard to protect the evidence and to leave nothing important behind. Throughout the process, investigators formulate theories about what happened. If they do their jobs well, they end up with a complete picture of the crime. In this chapter, I fill you in on exactly how investigators deal with evidence and crime scenes.

Assessing the Scene of the Crime

From the moment the first police officer arrives at the scene, he follows a strict set of procedural guidelines designed to protect him and everyone else who’s present; guard evidence against damage, contamination, or loss; and document everything that occurs at the scene. Following these procedures and maintaining control of the scene until the crime-scene investigators arrive offer the best chance of getting the evidence needed to identify and convict the perpetrator. Failure to follow these directives can result in the crime remaining unsolved or a known perpetrator walking free.

Distinguishing between primary and secondary crime scenes

There may be more to a crime scene than first meets the eye. In fact, more than one crime scene may exist, depending upon how the crime was committed, not to mention where. Crime scenes, therefore, are considered either primary or secondary. The primary crime scene is where a crime actually occurred. A secondary crime scene is in some way related to the crime but is not where the actual crime took place.

In a bank robbery, for example, the bank is the primary scene, but the get-away car and the thief’s hideout are secondary scenes. In the case of a killer who commits a murder in someone’s home but transports the victim’s body to a river for disposal, the victim’s home is the primary scene, and the killer’s vehicle and the point along the river where the body was dumped are secondary scenes.

Primary scenes typically yield more usable evidence than do secondary scenes, but not always. Sometimes the only crime scene investigators have to work with is a secondary scene, such as the place where a serial killer dumps a victim’s body, for example. Under these circumstances, investigators may not know where the actual murder took place and therefore use evidence they find at the secondary scenes to help them identify the killer or locate the primary scene. They may be able to use fibers from an expensive or unusual carpet they found on the victim to identify the manufacturer, the seller, and ultimately a list of buyers or locations where that particular product has been installed. Doing so can greatly narrow the focus of the investigation and lead police to the primary crime scene and the perpetrator.

Arriving at a crime scene

Regardless of whether the first officer to arrive at a crime scene found out about the crime via a phone call to the station, a radio call from a dispatcher, or directly from a concerned person, the officer must make every effort to detain the person who initially reported the crime and not allow that individual access to the crime scene. Anyone who reports a crime may have witnessed the incident or may have seen or heard something suspicious.

However, because the officer has no way of knowing whether the person reporting the crime is a witness or a suspect, allowing the informant access to the crime scene can mean losing or contaminating the evidence. After all, a perpetrator may

✔ Believe that reporting the crime makes him less likely to be a suspect

✔ Attempt to destroy or remove evidence

Neither of these situations is uncommon, so the officer who arrives first needs to approach the crime scene in a logical and organized manner, protecting the evidence and other people who may be there. Otherwise, harm may come to the officer, fellow officers, victims, witnesses, suspects, and even the perpetrator, or evidence may be damaged or destroyed.

The officer who responds first must make personal safety a primary concern and ensure that the perpetrator or perpetrators no longer are present or a threat. Whenever a perpetrator is present, the officer arrests and secures that person. Thereafter, the officer assists any victims who are present, offers first aid as needed, and mobilizes emergency medical services. After these important tasks are completed, the officer begins preserving the crime scene.

Additionally, the officer may need to detain suspects and witnesses and keep them separate to avoid collusion, meaning that the detainees work together to create a story to tell police. However, at this stage, the officer may not know who is who: A witness may become a suspect, and a suspect may actually be a useful witness. Furthermore, the officer may have no reason or legal right to detain some witnesses and thus must obtain accurate identification and contact information from each person who leaves the area.

At the heart of crime-scene protection is the principle of exchange. Locard’s Exchange Principle (see Chapter 1) states that when any two people come in contact with each other, they exchange or transfer trace materials, such as hair, fibers, and prints. Every person who enters the crime scene can leave behind evidence of his presence; take away crucial trace evidence on his shoes, clothes, or hands; or otherwise damage or alter any evidence that remains. Thus, access to the scene must be restricted immediately and denied to all witnesses and suspects.

Preserving and processing the scene

The size of a crime scene can vary greatly and the police must be prepared to quickly determine its boundaries. This task is not as easy as it seems. A crime scene may be a single room, an entire house, everything on a property, or even a whole neighborhood. And that’s just the primary scene.

At a minimum, the crime scene includes

✔ The exact spot where the offense took place

✔ Areas from which the site can be entered and exited

✔ Locations of key pieces of evidence, such as the body in a murder, a safe or cabinet in a burglary, or an entire structure in a suspicious fire

A crime scene can be cordoned off using crime-scene tape, barricades, automobiles, or even by police officers standing guard. Only personnel who are absolutely necessary for processing the scene are allowed in. This restriction often is more difficult to accomplish than you may think. A victim’s family members or neighbors may be emotionally unstable and thus difficult to remove from the area. And, of course, members of the press often have clever ways of gaining access to a crime scene, to say nothing of a captain or other high-ranking official trying to push her way past a lowly patrol officer who’s following orders to keep everyone without a reason for being there away from the scene. Furthermore, you can never underestimate the meanderings of the curious bystander.

After the scene is secured, the first officer to arrive establishes a security log, which basically is a sign-in sheet that must be signed by any and all visitors to the scene. This kind of crowd control helps the investigation in many ways, not the least of which is limiting the number of people who must be examined when stray fingerprints and shoeprints are found. If investigators can be ruled out, the print or prints remaining may point to the perpetrator.

A crime-scene investigator begins by doing a walk-through examination, getting a feel for the scene and organizing an approach to collecting evidence. During this overview, the crime-scene investigator typically doesn’t examine any

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