Evidence Report on Forensic Entomology
Crime Scene: #2
Evidence being examined: Insect found at crime scene
Forensic Science Used: Forensic Entomology
Summary of the Science:
Entomology is defined as the branch of zoology concerned with the study of insects. Forensic entomology concerns the application of this study to criminal or legal matters. Forensic entomologists study the insects found on or near remains to determine the relative time of death, if the body has been moved to a second site after death or if it has otherwise been disturbed, and to identify the presence and identity of certain chemicals found in the body. However, usually forensic entomologists' primary purpose in a criminal investigation is to determine the time of death or the post mortem interval (PMI). The earliest known use of forensic entomology in a criminal case was in 1247, in China, remembered in a book called The Washing Away of Wrongs or the Collected Cases of Injustice Rectified, written by the Chinese forensic medical expert Song Ci. In his book, Song Ci recounts a perplexing murder where the body was found in a rice field. The victim had been slashed multiple times, with what appeared to be a sickle. The local government was puzzled as to how to find the murderer, when so many workers used and owned a sickle. They gathered all the workers, and told them to lay their sickles on the grass. All the sickles appeared clean of blood or other bodily fluids. However, after a brief interval, a swarm of flies was quickly attracted to one sickle in particular. They could sense the presence of blood residue that the human eye could not detect. The owner of the sickle quickly confessed after confronted. This story is the first known instance of investigators using knowledge gained from insects to solve a crime. After the 13th century, scientists used and developed entomology to better understand the world: theories of spontaneous generation of maggots were dispelled by Francesco Redi, in the 19th and 20th centuries French and German physicians examined masses of corpses and discovered the relationship between decomposing corpses and certain insects, and in 1855 a French doctor was the very first person to use insect succession to identify the post mortem interval (PMI) or time of death. Subsequently, there were several other pioneers who developed this science and transformed it into modern forensic entomology.
Forensic entomology is comprised of 3 different subfields: urban forensic entomology, stored-product forensic entomology, and medico-legal forensic entomology. Urban forensic entomology usually concerns insect infestations in buildings, stored-product forensic entomology concerns the contamination of commercially distributed foods, and medico-legal forensic entomology concerns evidence that can be gathered from insects that is relevant to a crime. This report will specifically cover medico-legal entomology.
Medico-legal entomology is especially useful in determining the postmortem interval, the location of the crime, and specific chemicals that may have played a role in the crime. Evidence gathered using forensic entomology can be associative evidence, evidence that links a person or an item to a specific area. Insects exhibit a great amount of endemism, meaning certain insects occur only in well-defined areas. In addition, insects have a clear-cut phenology, meaning insects are only active in certain seasons or times of day. Both of these characteristics are very helpful when determining the time and location of death, and can link the crime to a place or to people or animals that could potentially introduce certain insects to the body. Locard's exchange principle states that every time a person exits or enters an area, material is deposited or removed. The same applies for corpses: when a corpse is moved from the original location of death, oftentimes insects feeding on the corpse are removed from that area as well, meaning investigators can use those insects to determine the original place of death.
When forensic entomologists analyze evidence, one main principle that they use when determining facts is faunal succession. Faunal succession is the order in which insects inhabit and feed on a corpse. Forensic entomologists use faunal succession especially to determine the post mortem interval. It also plays a factor in determining the location of the death. For example, certain insects appear only after a certain amount of time, which indicates the post mortem interval, and if certain insects appear on the body that are specific to a particular area, the location of the death is revealed and entomologists can estimate when the body was moved, based on faunal succession.
Insects that are relevant to an investigation and faunal succession include blood-feeding (haematophagous) insects that feed on live humans and corpse-feeding (necrophagous) insects. The primary blood-feeding insect relevant to an investigation is the mosquito. If even one mosquito is found on the body, investigators can extract the blood from it for a DNA sample for up to several days after the mosquito's bite. For corpse-eating insects, there are many varieties that change with different climates. The first responders to a corpse are usually flies, which include several different types. Then come beetles, mites, then moths. Finally, wasps, ants, and bees can found during any stage of decomposition, sometimes feeding on flesh but mostly preying on other insects eating the corpse.
Factors that impact faunal succession include moisture levels in the atmosphere, bodies of water, sun exposure, air exposure, and geography. Most of these factors affect faunal succession because of their effect on insect development. Large moisture levels slow development, as insects instinctively know to slow the rate of maturity until the conditions of their environment improve. On the other hand, small amounts of moisture act as an insulator and increase the speed of development. If a corpse is located on a body of water, the amount of insects feeding decreases because of insects’ unwillingness to traverse large bodies of water at their own risk, unless extremely motivated. As for sun exposure, the more exposure the faster the development. Insects are cold-blooded and benefit from increased amounts of warmth from the sun. Air exposure is more likely to deter insects. If a body is hanged and there is more air exposure, the corpse dries out faster and its fluids leak onto the ground, creating a less attractive meal to insects than if the corpse was not as exposed. However, insects can often be found on the ground where the fluids pooled. Finally, one other factor in faunal succession is geography. While most beetles and flies containing probative evidence live world-wide, some other species of insects can only be found in certain habitats. This affects the amount of information that can be gathered and the conclusions forensic entomologists draw.
The primary purpose of forensic entomology in criminal investigations is to determine the PMI (postmortem interval). Usually, forensic entomologists use flies, fly eggs, and fly larvae to estimate the postmortem interval. To determine the postmortem interval, forensic entomologists examine the flies and try to identify their species. Once this is done, investigators can study the development of the fly and use this information to make an educated guess on the number of days since death, based on the estimated arrival of the insect in question (faunal succession) and the number of days attributed to that specimen’s stage in development.
To identify the species of the fly, forensic entomologists can use scanning electron microscopy, potassium permanganate staining, analysis of the mitochondrial DNA, and analysis of the expression of different genes. The fastest and cheapest method of identification is potassium permanganate staining. For this method, you take the collected fly eggs, rinse them with a normal saline solution, and place them in a petri dish made of glass. You then soak the eggs in a 1% potassium permanganate solution for 1 minute, dehydrate them, and then mount them on a slide. Any light microscope can be used to examine the eggs and determine the species based on the dimensions of the egg.
Scanning electron microscopy is a method that was developed in 2007 that uses electron microscopy to single out irregularities like the presence or absence of anastomosis and holes, and the length and shape of the median area.
The method using mitochondrial DNA was developed in 2001. Basically, it uses DNA to identify the species of the insect. The same goes for the gene expression method, except this method analyzes how the genes of the specimen are expressed in its body.
After the species of the first responder is established, the species of the following insects can be identified to help understand the location of the death and the presence of chemicals in the body. Many of these insects can be identified through careful observation. If they are unrecognizable, one option is to grow them to maturity so they can gain more recognizable characteristics.
Many of the techniques mentioned above have only been around a couple decades or less. For example, scanning electron microscopy was first developed in 2007. This method allows for extremely high resolution visuals of a wide variety of samples. It is very versatile, and allows investigators to accurately identify the species of insects found on the scene. Currently, scientists are working on creating even higher resolution images.
At Crime Scene #2, one piece of probative evidence we found was an insect, which was crawling around in the bag of bones. The insect was picked up with a pair of tweezers and placed in an 80% alcohol and 20% water solution, which was then sealed. Afterwards, we picked up other insects and placed them in a container. The next day, we analyzed them. One of the bugs in the container was small, diamond-shaped, shiny, and jet black. Through these observations we identified the insect as a dermestid beetle. Once we identified the species we were able to use common guidelines accepted by the community of forensic entomology to determine the amount of time the insect was in the bag of bones, and by extension the age of the body. If a determestid beetle is found on a corpse, the state of its body can be an indicator of the amount of time it spent there. If a dermestid beetle is found completely dry, it usually indicates the beetle is 1-3 years old. If the fats of a dermestid beetle are rancid when found, it usually indicates the beetle is 3-6 months old. The dermestid beetle found in Case #2 was found completely dry, which suggests the beetle is 1-3 years old, and by extension the corpse. Through this evidence, our findings suggest that the unidentified person died 1-3 years ago.
Sources:
http://en.m.wikipedia.org/wiki/Forensic_entomology#History
http://www1.chinaculture.org/library/2008-01/31/content_26879.htm
http://insects.about.com/od/forensicentomology/p/early_forensic_ento_history.htm
http://en.wikipedia.org/wiki/Forensic_entomology#Forensic_entomology_subfields
http://en.m.wikipedia.org/wiki/Forensic_entomology#.28I.29_Blood-feeding_.28haematophagous.29_insects
Evidence being examined: Insect found at crime scene
Forensic Science Used: Forensic Entomology
Summary of the Science:
Entomology is defined as the branch of zoology concerned with the study of insects. Forensic entomology concerns the application of this study to criminal or legal matters. Forensic entomologists study the insects found on or near remains to determine the relative time of death, if the body has been moved to a second site after death or if it has otherwise been disturbed, and to identify the presence and identity of certain chemicals found in the body. However, usually forensic entomologists' primary purpose in a criminal investigation is to determine the time of death or the post mortem interval (PMI). The earliest known use of forensic entomology in a criminal case was in 1247, in China, remembered in a book called The Washing Away of Wrongs or the Collected Cases of Injustice Rectified, written by the Chinese forensic medical expert Song Ci. In his book, Song Ci recounts a perplexing murder where the body was found in a rice field. The victim had been slashed multiple times, with what appeared to be a sickle. The local government was puzzled as to how to find the murderer, when so many workers used and owned a sickle. They gathered all the workers, and told them to lay their sickles on the grass. All the sickles appeared clean of blood or other bodily fluids. However, after a brief interval, a swarm of flies was quickly attracted to one sickle in particular. They could sense the presence of blood residue that the human eye could not detect. The owner of the sickle quickly confessed after confronted. This story is the first known instance of investigators using knowledge gained from insects to solve a crime. After the 13th century, scientists used and developed entomology to better understand the world: theories of spontaneous generation of maggots were dispelled by Francesco Redi, in the 19th and 20th centuries French and German physicians examined masses of corpses and discovered the relationship between decomposing corpses and certain insects, and in 1855 a French doctor was the very first person to use insect succession to identify the post mortem interval (PMI) or time of death. Subsequently, there were several other pioneers who developed this science and transformed it into modern forensic entomology.
Forensic entomology is comprised of 3 different subfields: urban forensic entomology, stored-product forensic entomology, and medico-legal forensic entomology. Urban forensic entomology usually concerns insect infestations in buildings, stored-product forensic entomology concerns the contamination of commercially distributed foods, and medico-legal forensic entomology concerns evidence that can be gathered from insects that is relevant to a crime. This report will specifically cover medico-legal entomology.
Medico-legal entomology is especially useful in determining the postmortem interval, the location of the crime, and specific chemicals that may have played a role in the crime. Evidence gathered using forensic entomology can be associative evidence, evidence that links a person or an item to a specific area. Insects exhibit a great amount of endemism, meaning certain insects occur only in well-defined areas. In addition, insects have a clear-cut phenology, meaning insects are only active in certain seasons or times of day. Both of these characteristics are very helpful when determining the time and location of death, and can link the crime to a place or to people or animals that could potentially introduce certain insects to the body. Locard's exchange principle states that every time a person exits or enters an area, material is deposited or removed. The same applies for corpses: when a corpse is moved from the original location of death, oftentimes insects feeding on the corpse are removed from that area as well, meaning investigators can use those insects to determine the original place of death.
When forensic entomologists analyze evidence, one main principle that they use when determining facts is faunal succession. Faunal succession is the order in which insects inhabit and feed on a corpse. Forensic entomologists use faunal succession especially to determine the post mortem interval. It also plays a factor in determining the location of the death. For example, certain insects appear only after a certain amount of time, which indicates the post mortem interval, and if certain insects appear on the body that are specific to a particular area, the location of the death is revealed and entomologists can estimate when the body was moved, based on faunal succession.
Insects that are relevant to an investigation and faunal succession include blood-feeding (haematophagous) insects that feed on live humans and corpse-feeding (necrophagous) insects. The primary blood-feeding insect relevant to an investigation is the mosquito. If even one mosquito is found on the body, investigators can extract the blood from it for a DNA sample for up to several days after the mosquito's bite. For corpse-eating insects, there are many varieties that change with different climates. The first responders to a corpse are usually flies, which include several different types. Then come beetles, mites, then moths. Finally, wasps, ants, and bees can found during any stage of decomposition, sometimes feeding on flesh but mostly preying on other insects eating the corpse.
Factors that impact faunal succession include moisture levels in the atmosphere, bodies of water, sun exposure, air exposure, and geography. Most of these factors affect faunal succession because of their effect on insect development. Large moisture levels slow development, as insects instinctively know to slow the rate of maturity until the conditions of their environment improve. On the other hand, small amounts of moisture act as an insulator and increase the speed of development. If a corpse is located on a body of water, the amount of insects feeding decreases because of insects’ unwillingness to traverse large bodies of water at their own risk, unless extremely motivated. As for sun exposure, the more exposure the faster the development. Insects are cold-blooded and benefit from increased amounts of warmth from the sun. Air exposure is more likely to deter insects. If a body is hanged and there is more air exposure, the corpse dries out faster and its fluids leak onto the ground, creating a less attractive meal to insects than if the corpse was not as exposed. However, insects can often be found on the ground where the fluids pooled. Finally, one other factor in faunal succession is geography. While most beetles and flies containing probative evidence live world-wide, some other species of insects can only be found in certain habitats. This affects the amount of information that can be gathered and the conclusions forensic entomologists draw.
The primary purpose of forensic entomology in criminal investigations is to determine the PMI (postmortem interval). Usually, forensic entomologists use flies, fly eggs, and fly larvae to estimate the postmortem interval. To determine the postmortem interval, forensic entomologists examine the flies and try to identify their species. Once this is done, investigators can study the development of the fly and use this information to make an educated guess on the number of days since death, based on the estimated arrival of the insect in question (faunal succession) and the number of days attributed to that specimen’s stage in development.
To identify the species of the fly, forensic entomologists can use scanning electron microscopy, potassium permanganate staining, analysis of the mitochondrial DNA, and analysis of the expression of different genes. The fastest and cheapest method of identification is potassium permanganate staining. For this method, you take the collected fly eggs, rinse them with a normal saline solution, and place them in a petri dish made of glass. You then soak the eggs in a 1% potassium permanganate solution for 1 minute, dehydrate them, and then mount them on a slide. Any light microscope can be used to examine the eggs and determine the species based on the dimensions of the egg.
Scanning electron microscopy is a method that was developed in 2007 that uses electron microscopy to single out irregularities like the presence or absence of anastomosis and holes, and the length and shape of the median area.
The method using mitochondrial DNA was developed in 2001. Basically, it uses DNA to identify the species of the insect. The same goes for the gene expression method, except this method analyzes how the genes of the specimen are expressed in its body.
After the species of the first responder is established, the species of the following insects can be identified to help understand the location of the death and the presence of chemicals in the body. Many of these insects can be identified through careful observation. If they are unrecognizable, one option is to grow them to maturity so they can gain more recognizable characteristics.
Many of the techniques mentioned above have only been around a couple decades or less. For example, scanning electron microscopy was first developed in 2007. This method allows for extremely high resolution visuals of a wide variety of samples. It is very versatile, and allows investigators to accurately identify the species of insects found on the scene. Currently, scientists are working on creating even higher resolution images.
At Crime Scene #2, one piece of probative evidence we found was an insect, which was crawling around in the bag of bones. The insect was picked up with a pair of tweezers and placed in an 80% alcohol and 20% water solution, which was then sealed. Afterwards, we picked up other insects and placed them in a container. The next day, we analyzed them. One of the bugs in the container was small, diamond-shaped, shiny, and jet black. Through these observations we identified the insect as a dermestid beetle. Once we identified the species we were able to use common guidelines accepted by the community of forensic entomology to determine the amount of time the insect was in the bag of bones, and by extension the age of the body. If a determestid beetle is found on a corpse, the state of its body can be an indicator of the amount of time it spent there. If a dermestid beetle is found completely dry, it usually indicates the beetle is 1-3 years old. If the fats of a dermestid beetle are rancid when found, it usually indicates the beetle is 3-6 months old. The dermestid beetle found in Case #2 was found completely dry, which suggests the beetle is 1-3 years old, and by extension the corpse. Through this evidence, our findings suggest that the unidentified person died 1-3 years ago.
Sources:
http://en.m.wikipedia.org/wiki/Forensic_entomology#History
http://www1.chinaculture.org/library/2008-01/31/content_26879.htm
http://insects.about.com/od/forensicentomology/p/early_forensic_ento_history.htm
http://en.wikipedia.org/wiki/Forensic_entomology#Forensic_entomology_subfields
http://en.m.wikipedia.org/wiki/Forensic_entomology#.28I.29_Blood-feeding_.28haematophagous.29_insects