Chapter 08

Physical Evidence Collection and Preservation

Chapter 8

Objectives

• Describe steps (including preliminary assessment) to take to protect the scene and preserve evidence

• Describe the process of identifying evidence• Describe the proper process for collecting and

preserving evidence• Describe the processing of the evidence to

include the tagging, analysis, reports, and documentation of the chain of evidence

Case Study

• The cause of a fire was attributed to a light fixture overheating from a tenant covering it with a shirt to block the light

• A lawyer and a private investigator representing the renters wanted to see the evidence

• The bulb shown was actually the representative bulb and not the actual bulb

• The lawyer felt that the investigator was fabricating evidence

Introduction

• It is critical that each department or investigative division establish a physical evidence policy– Must cover all aspects of handling and storing

evidence for each incident– Policy is only as good as those who have input in its

creation– Everyone within the department must be trained on

the policy

Authority to Collect Evidence

• Public assigned fire investigator should collect any and all evidence that would be used as part of a hypothesis

• If a fire is accidental in nature, there is no crime– Must be cautious of unreasonable search and seizure

• Private investigators and insurance investigators have an entirely different set of rules

Protecting Evidence

• First responders are the first to encounter any evidence on the scene– Important to preserve all evidence

• Overhaul is the process of searching for hidden extension of the fire

• Salvage is a process of protecting items that have not been damaged

Securing a Fire Scene

Figure 8-1Commercialbarricade tapecan send a clearmessage to notcross the line.

Identifying and Collecting Evidence

Figure 8-3 A burnpattern can tell the story of the fire’s origin and direction of travel.

Residue Gases and Vapors

• Vapor density of the gas dictates whether the vapor settles into low areas or rises– Most lighter-than-air gases dissipate before a sample

can be taken

• Commercial sampling kits can provide vacuum containers

• Also can use devices that pull the air sample through a charcoal trap

Liquid Samples

Figure 8-4 A 1-gallon evidence can with debrisshould be filled no more than two-thirds to three-quarters full.

Solids

• Solid evidence is sometimes collected for verification of its identity

• Collecting solids requires precautions– Take care not to scoop up different types of solids

together– Wear double or even triple layers of latex gloves for

corrosive materials

Finding the Best Sample

• Leading edge of a floor burn or behind the baseboard that may have protected the accelerant product are both good locations

• Best “tool” to use to look for evidence is a properly trained K-9 accelerant dog– However, using a K-9 does not guarantee a positive

sample

Evidence Containers

Figure 8-6One-gallon metalpaint cans arethe containers ofchoice for mostinvestigators andlaboratories.

Traditional Crime Scene Forensics

Figure 8-7 Tool mark impressions on doors canindicate a forced entry or an attempt by someone to makeit look like there was forced entry.

Not-So-Traditional Evidence

Figure 8-8Appliances canbe involved in theignition sequenceand as such mayneed to be collectedas evidence.

Comparison Samples

• When there are indications of the presence of an accelerant, samples are taken to the laboratory – Samples taken from unburned, uncontaminated areas

are called comparison samples • Electrical switches, electrical circuit breakers, and even

electrical panels can all benefit from the collection of comparison samples

Contamination

• Anything introduced into the fire scene or into the evidence that makes test results unreliable– Sometimes occurs during suppression activities

• First responders need to concentrate on protecting what they find

Use of Gloves and Safety Gear When Collecting Evidence

• It is essential that all safety equipment be worn all the time

• Gloves protect your safety and also help you avoid contaminating any evidence

• All boots and gear must be thoroughly cleaned between each scene to prevent cross contamination

• Tools take special care

First Responder Considerations

• Proper training of suppression staff on evidence procedures helps to ensure preservation of evidence – If investigator not available, first responder can be

trained in evidence collection

• Chain of custody: method of documenting who had control from collection through trial

Documenting, Transporting, and Storing Evidence

• Documenting Evidence– Every piece of evidence collected by the investigator

must be tagged or labeled with:• Date and time collected, location, person who took it

• Case number

• Chain of custody

Shipment of Evidence

• Can personally deliver evidence• If a carrier is used:

– Pack to avoid damage in transit– Send registered, requiring a receiving signature

Evidence Storage

• Storage of evidence should be in a secure location where the investigator or lab personnel are the only persons having access

• Evidence rooms must be climate controlled to keep the environment dry and cool

Laboratory Testing

• Most frequent test requested by fire investigators is the testing of debris for presence of accelerants

• Common to run two tests together in a method called gas chromatography–mass spectrometry

• Best tool for success with testing at the laboratory is an open line of communications between lab personnel and fire investigators

Release of Evidence

• Evidence for either a criminal case or a civil suit may have to be kept for years, awaiting trial

• Not all evidence collected is used in trial– Prosecuting attorney decides

• In civil cases, if the investigator has been subpoenaed, all evidence must be kept the same as if for a criminal trial

Summary

• Evidence consists of a multitude of items from objects to patterns

• Critical that investigators know legal parameters about taking and securing evidence

• Once evidence has been collected, it should be locked up and secured

• Evidence should be processed for testing by a forensic laboratory as soon as practical

Chapter 08

Health & Medicine

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