Forensics Exam #4 Chapters 17, 18

Ion mobility spectrometer

A sample is introduced into an ionization chamber, where bombardment with radioactive particles emitted by an isotope of nickel converts the sample to ions. The ions move into a drift region where ion separation occurs based on the speed of the ions as they move through an electric field.

Conduction

Conduction is the movement of heat through a solid object. Poor conductors are called insulators. During a fire heat may transported through metals, such as nails, bolts, and fasteners to a location far from the initial heat source creating a new fire location

Convection

Convection is the transfer of heat energy by the movement of molecules within a liquid or gas. In a structural fire, hot gases move to the upper portion of the structure causing surfaces to pyrolyze and burst into a fire.

Flash over

Flashover occurs when all the combustible fuels simultaneously ignite to engulf the entire structure. •A fire that starts in one area of a structure could, through flashover, could create the illusion of or more unrelated fires, a sign mistaken for arson. •Irregular patterns are common in post-flashover conditions; hence, if the presence of ignitable liquids is suspected to have caused a fire pattern, supporting evidence from the laboratory for the presence of accelerant residues must confirm its existence. •Many factors can contribute to the deviation of a fire from normal behavior using burn patterns, such as depth of char, a V-shaped pattern, or low intense burn area, as indicators of a fire's origin can prove to be misleading when flash over has occurred.

Gas Chromatography

In the laboratory, the gas chromatograph is the most sensitive and reliable instrument for detecting and characterizing flammable residues.•The vast majority of arsons are initiated by petroleum distillates such as gasoline and kerosene. The gas chromatograph separates the hydrocarbon components and produces a chromatographic pattern characteristic of a particular petroleum product.By comparing select gas chromatographic peaks recovered from fire-scene debris to known flammable liquids, a forensic analyst may be able to identify the accelerant used to initiate the fire. The chromatographic pattern of the unknown is compared to patterns produced by known petroleum products.

Radiation

Radiation is the transfer of heat energy by electromagnetic radiation. A surface exposed to the heat of a fire may burst into flames when the surface reaches the ignition temperature.

The fire scene

The arson investigator needs to begin examining a fire scene for signs of arson as soon as the fire has been extinguished, perhaps even before.•Experience shows that most arsons are started with petroleum-based accelerants. The search of the fire scene must focus on finding the fire's origin, which may be most productive in any search for an accelerant or ignition device.

Collection and analysis

The entire bomb site must be systematically searched with great care given to recovering any trace of a detonating mechanism or any other item foreign to the explosion site.•Objects located at or near the origin of the explosion must be collected for laboratory examination. •Often a crater is located at the origin and loose soil and other debris must be preserved from its interior for laboratory analysis.•One approach for screening objects for the presence of explosive residues is the ion mobility spectrometer

Apparatus for Accelerant Recovery by Vapor Concentration

The vapor in the enclosed container is exposed to charcoal, a chemical absorbent, where it is trapped for later analysis.

Ink and Paper Comparisons

•A study of the chemical composition of the ink used on documents may verify whether or not known and questioned documents were prepared by the same pen; and the paper itself may be analyzed. •A nondestructive approach to comparing ink lines is accomplished with a visible-light microspectrophotometer.•Thin-layer chromatography is also suitable for ink comparisons.

High explosives

•Among the high explosives:-Primary explosives are ultra-sensitive to heat, shock, or friction and provide the major ingredients found in blasting caps or primers used to detonate other explosives. Secondary explosives are relatively insensitive to heat, shock, or friction and will normally burn rather than detonate if ignited in small quantities in the open air.•This group comprises the majority of commercial and military blasting, such as dynamite, TNT, PETN, and RDX. •Secondary explosives must be detonated by a primary explosive.•The speed of decomposition of high order explosions is known as detonation. Its extremely rapid producing a supersonic shock wave creating a blast effect with an outward rush of gases at speeds as high as 7,000 miles per hour. •In recent years, nitroglycerin-based dynamite has all but disappeared from the industrial explosive market and has been replaced by ammonium nitrate-based explosives.•High order explosives completely consume the explosive chemical compounds.

Digital Imaging Processing

•An image can be scanned by scanner or a digital camera and converting the image by computer into an array of digital intensity values called pixels.•Once the image has been digitized, an image editing program can be used to make adjustments such as lightening, darkening, color, and contrast controls. •Using a photo editor on a digitized image can reveal information that has been obscured.

characteristics from use

•As is true for any mechanical device, use of a printing device will result in wear and damage to the machine's moving parts.•These changes will occur in a fashion that is both random and irregular, thereby imparting individual characteristics to the printing device. •The document examiner has to deal with problems involving business and personal computers, which often produce typed copies that have only subtle defects.

Collection of Fire Scene Evidence

•At the suspect point of origin of a fire, ash and soot, along with porous materials which may contain excess accelerant, should be collected and stored in airtight containers such as new paint cans or wide-mouth glass jars, leaving an airspace to remove samples. Never use plastic containers to store fire scene evidence.•Collect samples from lowest debris layer •Collect unsuspected samples for comparison •Traces of flammable liquid residues may be located with a vapor detector (sniffer) or a trained canine.•The collection of all materials suspected of containing volatile liquids must be accompanied by a thorough sampling of similar but uncontaminated control specimens from another area of the fire scene, called a substrate control.

Effects of explosions

•Blast Pressure-Positive-Negative•Thermal/Incendiary•Fragmentation-Primary - Part of the Device-Secondary - Those around the Container

Oxidation

•Chemically, fire is a type of oxidation, which is the combination of oxygen with other substances to produce new substances.-Not all oxidation reactions proceed in a manner that one associates with a fire; e.g., rusting.-An oxidation reaction is associated with the concept of energy. Energy takes many forms; e.g., heat and light.-All oxidation reactions are examples in which more energy is liberated than what is required to initiate the reaction. These are known as exothermic reactions.

Search considerations

•Discarded Containers Used to Carry Accelerants•Shoe and Tire Impressions•Forcible Entry/Tools•Altered or Compromised Utility Appliances•Latent Prints•Run Off Water for Moved Evidence•Work from Least to Most Damaged•Location of Residence Vehicles/High Value Items

Alterations, Erasures, and Obliterations

•Document examiners must deal with evidence that has been changed in several ways, such as through alterations, erasures, and obliterations. •Erasures by rubber erasers, sandpaper, razor blade or knife to remove writing or typing disturb the fibers of the paper and are readily apparent when examined with a microscope under direct light or with side lighting. •If an alteration is made to a document with ink differing form the original, it can sometimes be detected due to differences in the ability of ink to absorb infrared light. •Obliteration of writing by overwriting or crossing out to hide the original writing can be revealed by infrared radiation, which may pass through the upper layer of writing while being absorbed by the underlying area.

Characters of handwriting

•Document experts continually testify to the fact that no two individuals write exactly alike. *•Many factors comprise the total character of a person's writing.•The early stages of learning handwriting are characterized by a conscious effort to copy standard letter forms. •However, as writing skills improve, nerve and motor responses associated with the act of writing become subconscious.•The subconscious handwriting of two different individuals can never be identical. •Variations are expected in angularity, slope, speed, pressure, letter and word spacing, relative dimensions of letters, connections, pen movement, writing skill, and finger dexterity.•Other factors to consider include the arrangement of the writing on the paper, such as margins, spacing, crowding, insertions, and alignment. •Spelling, punctuation, phraseology, and grammar can be personal and help to individualize the writer.•Furthermore, the writing style of one individual may be altered beyond recognition by the influence of drugs or alcohol.

Explosives

•Explosives are substances that undergo a rapid oxidation reaction with the production of large quantities of gases.•It is this sudden buildup of gas pressure that constitutes the nature of an explosion.•The speed at which explosives decompose permits their classification as high or low explosives.

Military and peroxide explosives

•In many countries outside the United States, the accessibility of military high explosives to terrorist organizations makes them very common constituents of homemade bombs.-R D X is the most popular and powerful of the military explosives, often encountered in the form of pliable plastic known as C-4.•Triacetone triperoxide (T A T P) is a homemade explosive that has been used by terrorist organizations.-T A T P can be made by combining acetone and peroxide in the presence of an acid.-Its existence has led to the banning of most liquids on commercial aircraft.

digital technology

•In the cases of photocopiers, fax machines, and computer printers an examiner may be called on to identify the make and model of a machine or to compare a questioned document with test samples from a suspect machine. •A side by side comparison is made between the questioned document and the printed exemplars to compare markings produced by the machine.•Examiners compare transitory defect marks, fax machine headers, toner, toner application methods, and mechanical and printing characteristics.

National Explosives Tracing Center,US Bomb Data Center

•Maintains database on all lost, stole, recovered explosives.•Commercial explosives tech bulletins•Military tech bulletins •Database on packaging, labeling, and markings

Types of explosions

•Mechanical - Overpressurization of compressed gas or liquids•Chemical - Compound or mixture which, upon the application of heat or shock, decomposes or rearranges with extreme rapidity, yielding much gas and heat.•Nuclear - Fusion or fission reaction

Improvised explosive devices

•Parts of an IED-Explosive charge-Fuzing system▪Mechanical such as a mousetrap▪Electrical such as a battery, cell phone, timer-Container•Methods of Initiation-Time - Elapsed time initiates the device- Action - Victim initiates the device-Command - Perpetrator initiates the device

Search considerations

•Perimeter•Geography and Weather•Packaging Materials•Recover items that don't belong such as single strand wires, switches, batteries, PVC, springs, tape, circuit board items•Swabbing items for residue•Crater samples ASAP surface and bottom

Blast trauma

•Primary - Wave causes injury•Secondary -Container shrapnel being propelled•Tertiary - Impact with other objects•Quartenary - Explosion related diseases such as COPD

Roll up safety considerations

•Secondary Explosions•Structural Hazards•Biohazards•Debris Hazards•Secondary Devices

Indicators of arson

•Some telltale signs of arson include evidence of separate and unconnected fires, the use of "streamers" to spread the fire from one area to another.-An irregularly shaped pattern on the floor resulting from the pouring of accelerant onto the surface. •Normally, a fire has a tendency to move in an upward direction, and thus the probable origin will most likely be the lowest point showing the most intense characteristics of burning. •Evidence of severe burning found on the floor (as opposed to the ceiling) of a structure is indicative of a flammable liquid. •Discovery of an ignition device: The most common igniter is a match, but arsonists can construct many other types of devices to start a fire, including burning cigarettes, firearms, ammunition, a mechanical match-striker, electrical sparking devices, and a "Molotov cocktail."

Handwriting exemplars

•The collection of an adequate number of known writings (exemplars) is most critical for determining the outcome of a handwriting comparison. •Known writing should contain some of the words and combination of letters present in the questioned document and be adequate in number to show the range of natural variations in a suspect's writing. •The writing implement and paper should also be alike.•The writing of dictation and several pages may serve to minimize attempts at deception

Lab recovery

•The easiest way to recover accelerant residues from fire-scene debris is to heat the airtight container in which the sample is sent to the laboratory.•When the container is heated, any volatile residue in the debris is driven off and trapped in the container's enclosed airspace. •The vapor or headspace is then removed with a syringe.•When the vapor is injected into the gas chromatograph, it is separated into its components, and each peak is recorded on the chromatogram. •In the vapor concentration technique, a charcoal strip is placed in the airtight debris container when it is heated.-The charcoal strip absorbs much of the vapors during heating.-The strip is washed with a solvent which will recover the accelerant vapors.-The solvent is then injected into the gas chromatograph for analysis.

Low explosives

•The most widely used explosives in the low-explosive group are black powder and smokeless powder.-Black powder is a mixture of potassium or sodium nitrate, charcoal, and sulfur.-Smokeless powder consists of nitrated cotton (nitrocellulose) or nitroglycerin and nitrocellulose. •Low explosives are confined to a container like a pipe. The speed of decomposition of low order explosions is called deflagration causing the walls of the container to fragment and fly outward in all directions.•Low order explosions do not completely consume the chemical compound of the explosive material.

Heat transfer

•The three mechanisms of heat transfer are conduction, radiation, and convection.

transcript comparisons

•The two requests most often made of the examiner in connection with the examination of photocopier, fax, and printing devices are:-Whether a particular suspect printing device can be identified as having prepared the questioned document-Whether the make and model of the printing devices used to prepare the questioned document can be identified

Combustion

•To start fire, the minimum temperature needed to spontaneously ignite fuel, known as ignition temperature, must be reached.•The heat involved when a substance burns is known as heat of combustion.•Once combustion starts, enough energy in the form of heat and light (flame) is liberated, a portion of which is used to sustain the fire. Fire is a chain reaction. •To initiate and sustain a fire, the following are required:-A fuel (vapor) must be present.-Oxygen must be available in sufficient quantity to combine with the fuel.-Heat must be applied to initiate the combustion, and sufficient heat must be generated to sustain the reaction.

Accelerant identification

•Typically a forensic analyst compares the pattern generated by the sample to chromatograms from accelerant standards obtained under the same conditions. •The pattern of gasoline, as with many other accelerants, can easily be placed in a searchable library. An invaluable reference known as the Ignitable Liquids Reference Hydrocarbon Collection (ILRC) is found on the Internet at http://ilrc.ucf.edu. •Complex chromatographic patterns can be simplified by gas chromatography/mass spectrometry