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Investigating Forensics

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SFU Museum of Archaeology & Ethnology, Burnaby, British Columbia

Investigating Forensics
The real science behind forensic investigation is explained by scientists and police in a tour through the specialist laboratories at the Centre for Forensic Research at Simon Fraser University.
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Learning Object Collection: Investigating Forensics
Forensic Entomology
Once a person dies his or her body starts to decompose. The decomposition of a dead body starts with the action of microorganisms such as fungi and bacteria, followed by the action of a series of insects (arthropods). Bodies decompose slowly or fast depending on weather conditions, if they have been buried or are exposed to the elements, if there is presence of insects or if they have a substance in their bodies that prevents their fast decomposition such as body size and weight, clothing,

The dead body goes through constant changes allowing investigators to estimate how long that person has been dead. Generally speaking, there are 5 basic stages of decomposition:
Fresh, putrefaction, fermentation, dry decay and skeletonization. Every stage attracts different kinds of organisms that will feed off the body and recycle the matter. These stages may takes days or years (even thousands of years!)
Insect Informants
Adult blow flies (Calliphoridae)
Adult blow flies (Calliphoridae) raised from larvae collected from a body at a crime scene. These flies are identified under a dissecting microscope in the laboratory in order that they can be used to estimate elapsed time since death.

The Critical Thinking Consortium, Simon Fraser University




© 2011, SFU Museum of Archaeology & Ethnology. All Rights Reserved.
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Learning Object Collection: Investigating Forensics
Learning Object: Insect Informants
Use of Insects in Death Investigations
It is by collecting and studying the insects that are feeding on a body that a forensic entomologist can estimate the time elapsed since the person died. Flies have great powers of dispersal and they rapidly discover bodies, usually ahead of beetles. Blow flies provide the most accurate estimation of time since death. However many other species of flies, beetles and arthropods may also be found at a death scene. Beetles usually occur at later stages of decomposition. As the corpse dries, it becomes less suitable for the blowflies, flesh flies and house flies that like a semi-liquid environment. The cheese flies, coffin flies, are abundant as the corpse dries. Eventually, the corpse becomes too dry for the mouth hooks of maggots to operate effectively. The hide beetles, ham beetles and carcass beetles, with their chewing mouthparts, devour the dry flesh, skin and ligaments. Finally, moth larvae and mites consume the hair, leaving only the bones.
Blow fly (Calliphoridae)
Blow fly (Calliphoridae)
Blow fly (Calliphoridae) larvae in vials of alcohol for permanent preservation. Larvae are first heat killed in hot water for 5 minutes to destroy the internal enzymes then placed in alcohol. They can be kept in this manner forever. Insects collected from a crime scene are kept forever for eventual use in court.

The Critical Thinking Consortium, Simon Fraser University




© 2011, SFU Museum of Archaeology & Ethnology. All Rights Reserved.
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Learning Object Collection: Investigating Forensics
Learning Object: Insect Informants
Estimating Time elapsed since death or Post Mortem Interval
There are two methods to estimate time since death: 1) using successional waves of insects and 2) maggot age and development. Insect succession is used if the individual has been dead for a month or longer. Maggot development is used when death occurred less than a month prior to discovery.

1- Insect succession uses the fact that a body (human or otherwise) supports a rapidly changing ecosystem as it decomposes. As they decay, the remains go through physical, biological and chemical changes, and different stages attract different species of insects.

2 - Maggot age and development is used in the first few weeks after death and can be accurate to a few days or less. Maggots are immature flies and Calliphoridae (blow flies) are the most common insects used.
Collecting, Preserving and Packaging Specimens
Forensic investigations rely on evidence and material found at a crime scene, which must be recorded and collected carefully. If the scene is outdoors, forensic entomologists note the landscape, plants and soil types, as well as the weather. Temperature is especially important and a portable recording device is left to record long term changes. A soil sample is often taken, since larvae may wander away from the body to pupate. If the scene is indoors, an investigator looks for access points where insects could get in. The forensic entomologist takes samples from different areas of the body. Some of the maggots are collected, placed in boiling water and preserved in alcohol to stop development. Other maggots are collected alive and kept until they reach adulthood. Eggs are only collected if there are no later stages associated with the body. Empty pupal casings are also collected. Adult flies are useful only if the wings are crumpled. As recently emerged they can be linked to the body.
Live blow fly larvae
Live blow fly larvae
Live blow fly larvae are raised in glass jars with sawdust to mimic the soil and beef liver on a paper towel to mimic the carrion. These are then placed in an incubator in order to control for temperature, lighting and humidity.

The Critical Thinking Consortium, Simon Fraser University




© 2011, SFU Museum of Archaeology & Ethnology. All Rights Reserved.
View the complete media file

Learning Object Collection: Investigating Forensics
Learning Object: Insect Informants
Use of Insects in Death Investigations
It is by collecting and studying the insects that are feeding on a body that a forensic entomologist can estimate the time elapsed since the person died. Flies have great powers of dispersal and they rapidly discover bodies, usually ahead of beetles. Blow flies provide the most accurate estimation of time since death. However many other species of flies, beetles and arthropods may also be found at a death scene. Beetles usually occur at later stages of decomposition. As the corpse dries, it becomes less suitable for the blowflies, flesh flies and house flies that like a semi-liquid environment. The cheese flies, coffin flies, are abundant as the corpse dries. Eventually, the corpse becomes too dry for the mouth hooks of maggots to operate effectively. The hide beetles, ham beetles and carcass beetles, with their chewing mouthparts, devour the dry flesh, skin and ligaments. Finally, moth larvae and mites consume the hair, leaving only the bones.
Transferring blow fly larva
Transferring blow fly larva
Placing blow fly larva into an exhibit vial of alcohol, after first heat killing with hot water to enhance preservation.

The Critical Thinking Consortium, Simon Fraser University




© 2011, SFU Museum of Archaeology & Ethnology. All Rights Reserved.
View the complete media file

Learning Object Collection: Investigating Forensics
Learning Object: Insect Informants
Other types of information are important
Other types of information are also important. For the site, this includes:
1. the habitat (woods, beach, a house)
2. the site (shady or exposed to sunlight)
3. the vegetation (trees, grass, bush, shrubs)
4. the soil type (rocky, sandy, muddy)
5. the weather at the time of collection (sunny, cloudy)
6. the temperature and humidity
7. the elevation and map coordinates of the scene
8. unusual details (like whether the body was submerged)

For the remains, it is helpful to know:
1. the presence, extent and type of clothing on the body
2. if the body was covered or buried (and with
what)
3. if there is an obvious cause of death
4. if there are wounds on the body or body fluids (blood etc) at the scene
5. if drugs were involved
6. the position of the body
7. what direction the body faced
8. the state of decomposition
9. if other carrion was found in the area that might also attract insects
10. if the body was moved or disturbed
Forensic archaeology - a clandestine grave
Archaeologists removing surface vegetation from a suspicious area
Removing recent plant growth can reveal the limits of a clandestine grave, allowing archaeologists to excavate very precisely.

The Critical Thinking Consortium, Simon Fraser University




© 2011, SFU Museum of Archaeology & Ethnology. All Rights Reserved.
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Learning Object Collection: Investigating Forensics
Analysis
At the laboratory, entomologists measure and examine immature specimens, placing them in a jar with sawdust and food. The insects are checked frequently and when they pupate they are removed. The date of pupation and emergence is noted for each specimen. When the adults emerge, they are killed and stored. This process is important because adult flies are much easier to identify to species than larvae. Also, pupation and emergence times are used to calculate the age at the time of collection.
Other Uses for Forensic Entomology
Forensic entomology is used most commonly to determine time since death. However, insects can provide other important information about a crime or victim, or a person's life before they died. The use of drugs can change the lifecycle timing of an insect. One such drug is cocaine, which causes the maggots feeding on affected tissues to develop much faster than they normally would.

Flies tend to lay their eggs first in moist places in the body like the eyes and mouth. If eggs or maggots are found on normally dry skin, like the forearms, before these other areas, it suggests that the skin was damaged in some way. This may be because the individual injured themselves in a fall or because they were trying to protect themselves from a weapon.

The species of insect can point to events that occurred after death. If a species that is normally found only in the countryside is found at a scene in the city, it suggests the body has been moved at some point after death.
A pinned fly
A pinned fly
A pinned fly raised from a larva or maggot from a homicide victim.

The Critical Thinking Consortium, Simon Fraser University




© 2011, SFU Museum of Archaeology & Ethnology. All Rights Reserved.
View the complete media file

Learning Object Collection: Investigating Forensics
Learning Object: Insect Informants
Limitations of Forensic Entomology
Although forensic entomology is a powerful tool for investigators, this science is not infallible. For example, time of death estimates depend on accurate temperature information, but local weather patterns can be variable and data may come from stations quite distant from the crime scene. Also forensic entomology relies on insect abundance. In winter, there are fewer insects and entomology's use is limited. In addition, since it takes time to rear insects, forensic entomology cannot produce immediate results. Also, treatments (like freezing, burial or wrapping) that exclude insects can affect estimates. Finally, since chemicals can slow or accelerate growth, insect evidence may be affected by the presence of drugs in a corpse's system.
Report writing
A report is a formal description of an event or investigation. A forensic report explains what an investigator did, how they did it and what they think the evidence shows. It is of crucial importance because it must be able to explain the results of the investigation to a judge and possibly a jury who would not be able to attend a crime scene and observe an investigation first-hand. There are no agreed-upon protocols or standards for writing forensic reports in Canada, but most forensic scientists use a scientific format that includes the following:

- Report summary
- Background (how the author became involved in the case)
- Qualifications of the author (what makes the author an authority on the subject)
- Materials, methods and limitations (what work was done, how and why it was conducted, and any barriers to further investigation/analysis)
- Results (what the evidence found)
- Interpretation of results (what the evidence means, within the area of expertise)
- Conclusions

Learning Objectives

Forensic entomology is the study of insects for medico-legal purposes. There are many ways insects can be used to help solve a crime, but the primary purpose of forensic entomology is estimating time since death.

In this Learning Object Collection you will find information about the forensic entomology, how is it practiced at Simon Fraser University's Centre for Forensic Research, the relationship between entomological evidence and clandestine graves, how insect evidence is used to estimate time elapsed since death and the limitations of forensic entomology. A series of extended lessons with charts and supplemental materials created by The Critical Thinking Consortium is available on the Investigating Forensics web site (www.sfu.museum/forensics ).

After using this object students will be able to:
- describe the use of insect evidence in death investigations
- describe the life cycle of blow flies and relate this cycle to the process of establishing elapsed time since death
- explain how insect evidence is collected at a clandestine grave and preserved for use in the lab
- demonstrate an understanding of the use of a scientific reference collection
- evaluate the limits of forensic entomology in specific cases.