Forensic science the basics chapter 2

Trace evidence

(hair, fiber, small paint chips, or glass) should be placed in an envelope or plastic baggie sealed on all sides. It is not recommended to use tape to hold this evidence (commonly called a "tape lift"). The glue in the tape can interfere with the chemical analysis of the evidence and the evidence may be difficult to remove from the tape. Evidence can be put in a druggist's fold (also called an evidence fold) and then put into a tamper-evident envelope. A druggist fold is a piece of paper folded in such a way as to keep the evidence from leaking or falling out.

Chain of custody: Rules of evidence in federal and every state court in the United States require that all evidence be authenticated. Authentication requires:

1. A record of who is in possession of the evidence from the time it is collected at the crime scene until the time it is delivered to court. This detailed record is called the chain of custody. 2. The evidence must also be uniquely identified (e.g., using a bar code) in such a way so that it cannot be confused with any other piece of evidence and so that it can be shown that the evidence being used in court is the same evidence that was taken from the crime scene. 3. The evidence must also be packaged in tamper-evident packaging. This is both a document and a process that insures the integrity of the evidence. If the chain of custody has a substantial break—one that would seriously call into question the quality or integrity of the evidence—the evidence may be ruled inadmissible in court.

There are three ways that crimes are discovered:

1. A witness sees a crime in progress and reports it to the police. 2. The victim of a crime reports it to the police. 3. The police discover a crime in progress.

First Officer at the Crime Scene

1. Ascertain whether the perpetrator is still at the scene 2. Tend to the injured 3. Notify supervisors, medical examiner, crime scene team, or other personnel 4. Secure consent or a warrant to search the scene: 5. Secure the scene 6. Avoid walking through the scene and searching for evidence 7. Note any obvious safety hazards:

Timing:

A historical scene changes all the time, especially if it is outdoors. For ancient ruins, this may not be too important in the short run. A couple of weeks of delay in searching a ten-thousand-year-old village will probably have little consequence. For crimes that occurred only a few hours or days ago, however, time may be of the essence. For example, if a burglary is not discovered and solved within an hour after it occurs, research has shown that it probably never will be. The trail gets cold really quickly. Plan of attack: There must be a plan for systematically searching the site that ensures that no stone is left unturned without needlessly covering the same area again and again.

Chain of custody:

A physical log for a single piece of evidence that documents who had possession of the evidence and when the evidence was in his or her possession. It is a flowchart of the movement of evidence from collection to processing at the crime lab to presentation in court

Probative:

A piece of evidence that tends to prove or disprove a fact or assertion.

Controlling the scene

Contamination must be minimized by permitting access to the site to as few people as possible. Additionally, those persons at the scene may be asked to give elimination samples if necessary to compare with collected evidence. For example, CSI team members may be asked for samples of their DNA

The basic steps in crime scene investigation include

Discovery of the crime First officer responds Crime scene protocol Preliminary scene examination Systematic search Documentation Evidence collection and preservation Reconstructing the crime

Authentication:

Documenting who has possession of crime-related evidence from the point of collection to its appearance in a court of law

Documentation:

Every instance of searching an historical site further changes it. Evidence is found and then is moved or removed. Gathering evidence is a vital part of learning the story of the site. Once it changes, it will never be the same again. This is an important concept in searching a crime scene. The crime scene must be documented thoroughly so that a record can be made of its condition when the crime occurred. This includes labeling the location of each piece of evidence when it is discovered. Ultimately, the evidence will be useful in establishing that a crime has actually occurred and someone must be prosecuted for it, a process called corpus delicti

Search methods:

Evidence may be located using a systematic approach to survey the site. These methods employ spiral, grid, line, or zone techniques.

Photographs are taken in an organized manner

First, the entire scene is photographed from each corner of the structure, room or object. Then the item of interest is photographed from a distance, mid-range, and then close-up with and without a scale in the picture. Figure 2.5 shows outside and interior room photography. Figure 2.6 illustrates photography of a victim.

Protocol:

In criminal investigations, protocol is an established, detailed plan or procedure that must be implemented for evidence to be valid.

Sting operation:

Law enforcement agents stage a scenario whereby criminals are encouraged to commit crimes that they would probably have committed anyway.

Appropriate personnel

Only highly qualified, trained personnel should conduct the search of the site.

Postmortem Interval (PMI):

Postmortem interval is the length of time from discovery of a dead body to the time the victim died.

Safety issues

Safety of the scene searchers must be considered. Hazards at the ancient remains of a city are going to be different from those at a modern crime scene, although the flooring in a house that had major fire damage may be just as unstable as the ancient ruins of a building.

Druggist's fold (or evidence fold):

Small pieces of evidence are packaged in druggist folds (papers) to ensure that they are not lost. They are sometimes also referred to as "evidence folds." The folded paper is then placed in standard evidence packaging.

Tamper-evident packaging:

Specific types of containers or packages for crime scene evidence that have seals that can only be opened by tearing or cutting, thereby giving proof of access

Corpus delicti:

The Latin translation is "body of crime." Corpus delicti means that it must be proven that a crime has occurred before an individual can be convicted of committing a crime. For example: A death must be ruled a homicide before anyone can be tried for murder or a fire must be ruled as an arson in order for a person to be tried for setting the fire.

Modus Operandi (MO):

The Latin translation means "mode of operation." This refers to the style or method that a criminal uses when committing a crime. For repeat offenders, an MO may assist investigators in locating the suspect due to his or her characteristic way of committing the crime.

chain of custody

The chain of custody begins when the evidence is discovered.

First responder:

The initial police officer at the crime scene is regarded as the first responder

Exemplars:

These are baseline, known evidence such as fingerprints, DNA, hair, or voiceprints collected from suspects or victims in order to compare with evidence taken from a crime scene. Exemplars are sometimes referred to as "knowns" or "controls

Living plants (marijuana) must be packaged

breathable" containers such as paper bags. If the plants are packaged in airtight containers, they will rot and may become useless.

two basic methods of documenting a crime scene

first was making a sketch of the crime scene, while the second was using photography to document a scene

four basic types of search methods

if the entire crime scene is one room of a house, a search may begin at one end of the room and proceed in a spiral fashion toward the center or may be a back-and-forth (line) pattern across the room. If the scene includes several rooms, each one is searched systematically using a zone method. If the scene is outdoors in a large area, it may be necessary to divide the scene into grids and then search each grid.

Fire residue

must be put in an airtight container. Unused paint cans are best. If fire residue is put in breathable containers, the accelerant will evaporate.

Three major steps in the process of evidence collection

recognition, collection, and packaging/preservation

Wet paint

should be allowed to dry or packaged in breathable container

Biological evidence

should be allowed to dry or, if packaged wet, the container must be breathable. Blood can also be packaged in a glass or plastic culture tube that contains a preservative, usually ethylenediamene tetraacetic acid (EDTA).

Small amounts of powder

should be put in paper with a druggist's fold and then an envelope or baggie.

Two of the most important elements of the chain of custody

tamper-evident packaging and the custody form

fingerprints

typically the last evidence taken at the scene due to possible contamination of fingerprint dust with other crime scene evidence.