Source: bioquipinc.com
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Forensic scientists are often called into court to act as expert witnesses. In addition to their verbal testimony, witnesses may use visual representations such as exhibit boards (similar to large posters) or electronic technology such as PowerPoint. The impact of an expert’s testimony is enhanced through the use of effective visual representations. Exhibit boards provide the judge and jury with relevant background information about forensic methods as well as details of a particular case.
In this activity, you will work in groups and create exhibit boards to support a forensic entomologist’s testimony about the estimated date of a victim’s death.
First, you will read the two texts presented on the following pages. The first text describes in detail some of the forensic entomology methods used in investigations. Use the Gathering the Information table below to highlight key pieces of information in the article and summarize those ideas, in your own words, in the first column of the chart.
The second text is a description of an actual case. Use the second column of the chart and enter important case details there, beside any related points in column one.
Review columns one and two on your chart and discuss which pieces of information might be included on the exhibit boards. Select information that might require clarification or explanation and is critical to the testimony. Then brainstorm ways to convey the information (lists, diagrams, drawings, etc.) and record these in column three before creating your posters.
Activity from the SFU Museum of Archaeology and Ethnology, Simon Fraser University
Do this exercise with your team and then present your findings to your teacher and other teams.
TIP
You can re-use this exercise as part of your project. Fill in with your own information about your investigation
A pinned fly raised from a larva or maggot from a homicide victim.
| KEY INFORMATION FROM THE ARTICLE | KEY POINTS FROM THE ACTUAL INVESTIGATION | IDEAS TO INCLUDE ON THE EXHIBIT BOARDS |
|---|---|---|
Adapted from Anderson, G. S. FORENSIC ENTOMOLOGY: THE USE OF INSECTS IN DEATH INVESTIGATIONS
Among the tasks tackled by a forensic entomologist is the analysis of the insects on or inside a corpse to determine how much time has passed since the person died. In addition to carefully collected insect samples, the entomologist uses information such as the environment at the crime scene, the cause of death and the average temperature in the area, to produce an accurate estimate.
There are two main methods used to analyze the insects from a body
Method 1 is most useful when the person has been dead from a few weeks up to a year or sometimes more. It works because human bodies change as they decompose. Some types of insects are attracted to the earliest stages of decomposition while others arrive on the scene much later. Because insects typically inhabit a corpse in predictable "waves" of different species, forensic entomologists can use the presence of a particular type of insect to estimate the time of death.
Method 2 can give a date of death accurate to a day or less, or to a range of days using the age and developmental stage of immature blowflies (or maggots). As tissues of the corpse decompose, the remains go through rapid physical, biological and chemical changes, and different stages of the decomposition are attractive to different species of insects. Certain species of insects are often the first witnesses to a crime.
Blowflies are common insects that are attracted to a corpse very soon after death and are usually the first to arrive. They lay their eggs on the corpse, usually in a wound if present or, if not, in any of the body’s natural openings. The eggs hatch and the immature insects go through various stages of development at predictable times.
This time period is affected by the availability of food and the temperature. In the case of a human corpse, food availability is not usually a limiting factor, so temperature is the strongest influence. Since insects are “cold blooded,” their development is extremely temperature dependent, that is, the warmer the temperature, the faster rate of development, and vice-versa.
Rates of development for Calliphora vicina, a species of blowfly [inserted from another source by the same author]
| 15.8°C | 20.7°C | 23.3°C | ||||
|---|---|---|---|---|---|---|
| Time to reach stage (hours) | Time to reach stage (hours) | Time to reach stage (hours) | ||||
| Stage | Min | Max | Min | Max | Min | Max |
| 1st instar | 40.6 | 44.4 | 20.9 | 23.6 | 21 | 22 |
| 2nd instar | 94.3 | 103.3 | 52.3 | 52.3 | 45 | 45 |
| 3rd instar | 135.7 | 158.7 | 78.3 | 95.3 | 77 | 77 |
| Prepupal | 233.7 | 246.7 | 127.9 | 145.3 | 145 | 159.5 |
| Pupal | 382.3 | 392.3 | 245.7 | 356.9 | 264 | 270 |
| Adult | 775 | 917 | 486.2 | 647.8 | 468.5 | 624.5 |
The above data has been adapted from: Anderson, G.S. 2000 "Minimum and maximum development rates of some forensically important Calliphoridae (Diptera)", Journal of Forensic Science, Vol. 45(4), pp. 824-832, and simplified for this lesson. (Taken from http://www.clt.uwa.edu.au/data/page/112507/fse07_forensic_entomology.pdf)
Calliphora vicina
Source: Wikipedia.org
An analysis of the oldest life stage of blowfly on the corpse and the temperature of the region in which the body was discovered leads to a day or range of days for the 'time since death'. For example, if the oldest insects are 7 days old, then the deceased person has been dead for at least 7 days. This method can be used only until the first adults begin to emerge, in which case dark pupae are present. After that, it is not possible to determine which generation of flies is present. In this case, the time of death must be determined using the second method, that of insect succession.
Developmental stages of a blowfly
Adapted from Anderson, G. S. Forensic Entomology: The Use of Insects in Death Investigations
Human remains were found in mid-October. The death was due to gunshot wounds to the head. The upper portion of the body was almost skeletonized (reduced to skeleton), but the lower area, clad in tight clothes, appeared almost fresh. There were several large maggot masses on the corpse that generate their own heat for a while due to the frenzied activity. The temperature of the largest maggot mass was 20°C, even after the body had been refrigerated at 4°C for two hours. All sizes of larvae were collected and three pupae. (Refer to the insect life cycle above to see these stages). These were pale in colour so had only just pupated (become pupae). No puparia (the rigid outer shell that covers some pupae) were found. The mean temperature at the death site was 15°C.
Two species of blowfly emerged, Calliphora vomitoria and Phormia regina. Both are common species that are amongst the first to arrive on a corpse. The oldest stage of Calliphora vomitoria collected was just entering the prepupal stage of the third instar (the last stage before the larva turns into a pupa). This was determined from size, number of spiracular slits (breathing holes), date of pupation and behaviour. At the temperature of the death site, 15°C, Calliphora vomitoria takes a minimum of 9.3 days to reach the beginning of the prepupal stage of the third instar. So these insects were a minimum of 9 days old when collected on 12 October, meaning that they were laid as eggs on or before 4 October. As there was blood at the scene, the insects probably arrived very soon after death. Therefore, death must have occurred on or before 4 October.
Using the same techniques for Phormia regina, the oldest specimens of which were in the pupal stage when collected, it was calculated that Phormia regina eggs were laid no later than 3 October. Therefore, using the two insects together, it can be shown that death occurred on or before 3 October.
The use of forensic entomology may me positive for your project, both for the investigation fila and the oral presentation. Learn as much as you can from this session and the below videos.
Watch this video about the Kirk Odom case and answer the questions below.
1. Kirk Odom was accused of...
2. Why were the police initially looking at Odom for this crime?
3. Which of the following is TRUE?
4. What did the FBI’s forensic scientists analyze when performing microscopic hair analysis?
5. The most damning evidence in Kirk Odom’s case was...
6. Kirk Odom...
7. Houck’s analysis showed that in about 11% of the cases, ...
8. Which of the following is true?
9. Which of the following is NOT true about the three cases featured in the Washington Post article?
10. The FBI is now reviewing how many cases involving hair analysis?
Video from retroreport.org
Do this exercise and then discuss your answers with your nearest classmate.
Send your guesses to your teacher, using the dedicated iDoceo Connect platform (only for groups specified above).
Definitions adapted from A Dictionary of Forensic Science by Suzanne Bell.
Play with three or four other classmates.
Source: pinterest.com
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