Within the United States and around the world, insect scientists (entomologists) are being called upon with increasing frequency to apply their knowledge and expertise to criminal and civil proceedings and to become recognized members of forensic laboratories and medical/legal investigation teams. Insect evidence gathered from and around the corpse, when properly collected, preserved and analyzed by an experienced and appropriately trained forensic entomologist, can provide an objective estimate of the time of death as well as other valuable information concerning the circumstances surrounding the victim's demise.
INSECTS AND HUMAN DECOMPOSITION
Human corpses, whether they have been produced naturally or as the result of foul play, are processed by insect decomposers in the same manner as any other piece of carrion. Forensic entomology, therefore, is based on the analysis of the insects and other invertebrates which sequentially colonize a corpse as decomposition progresses and on the rates at which the various stages of their offspring develop. Entomological information can be extremely useful in determining manner of death, movement of the corpse from one site to another, and length of the postmortem interval. The following case history studies are described to illustrate this use.
While a wide variety of insect species are attracted to decomposing remains and play an active role in the decay process, two groups, the flies (Diptera) and beetles (Coleoptera), are of major importance in most circumstances. Diptera, whose larvae are capable of living in a semi-liquid medium, are the first insects to be attracted to and to colonize decomposing remains. Fly larvae (maggots) are responsible for the dramatic consumption of the corpse's tissues. Only much later, when the corpse has to a large extent dried out, do species of other insect groups, notably beetles, move in and continue the process.
Case No. 1
On 4 June the partially clad body of a young female was found alongside a rural highway in the northwestern United States. An autopsy revealed that she had died of multiple head and neck wounds inflicted by a heavy sharp object. She was subsequently identified as a 14-year old prostitute. Her brother reported her as missing approximately four days prior to discovery of her corpse.
She had last been seen alive on the morning of 31 May in the company of a 30-year old army sergeant, the primary suspect. While considerable circumstantial evidence supported the theory that the victim had been murdered by the sergeant, an accurate estimation of time of death was crucial to establishing a possible link between the suspect and the victim at the time when death occurred.
Several estimates of postmortem interval were offered by medical examiners and investigators. These were based largely on the physical appearance of the body and the extent to which decompositional changes had occurred in various organs. They were not based on any quantitative scientific methodology.
Numerous fly larvae (maggots), adult flies, and other insects were observed and collected in and around the victim's wounds. Some were placed alive in small containers and subsequently reared to produce adult flies. Others were placed immediately into a liquid preservative. Additional specimens collected at the autopsy were processed in a similar manner. Numerous photographs of the crime scene, the surrounding vegetation and terrain, and the corpse were taken. These photographs included enlargements illustrating the adult flies and maggots present at the time the body was discovered.
Reports describing the condition of the body when found and detailing autopsy procedures and results also were reviewed. Climatological data, including maximum and minimum temperatures, incidence of rainfall, cloud cover, wind speed and direction, and relative humidity, were obtained from a government weather station located a short distance from where the victim was found. These data indicated the environmental conditions to which the remains and its insect associates were exposed.
Based on this total array of evidence, entomologists determined that the first insects to colonize the remains had arrived on 31 may. The insect evidence indicated a PMI of four days.
Based on this evidence, the army sergeant with whom the victim had been last seen alive was arrested and charged with first degree murder. On questioning he admitted to having murdered the victim by striking her six to eight times with a small hatchet sometime around noon on May 31. Subsequently, he entered a plea of guilty to the murder charge and was sentenced to life in prison without parole.
THE IMPORTANCE OF BLOW FLIES
Fly species differ in abundance from region to region, from habitat to habitat, and from season to season. In the northern United States for example, a blue bottle fly, Calliphora vicina, is more abundant during the cooler parts of the year, whereas a green bottle fly, Phaenicia sericata, dominates corpses during the warmest parts of the summer. Another green bottle fly, Lucilia illustris, frequents corpses located in open, brightly lit habitats, whereas the black blow fly, Phormia regina, prefers shade.
Case No. 2
The remains of a murder victim were reportedly thrown down an open well on a small farm in a rural area in south-central Indiana. Then the well was completely filled with junk, tires, and rocks. The exact location of the well where the remains were deposited was unknown, but as the investigators drove into one of several wooded farm yard sites being investigated, it was obvious they had found the right location. Several thousand flies were hovering over a pile of old tires. The remains were found at the bottom of the well under the debris. Decomposition was advancing in the body, but there were no insects found on it. Access to the body by the blow flies was prevented by the intervening material, but odors were still capable of attracting multitudes of insects.
Case No. 3
Recently, in New England, the fully-clothed body of a young adult woman was found in a parking lot located behind an urban industrial complex. The victim had died from a single, 9mm bullet wound to the right temple, and a substantial pooling of blood was noted beneath the victim's head. The body was discovered initially by employees reporting for work at approximately 6:00 a.m. No insect evidence was observed on or around the body during the preliminary crime scene survey. As the investigation proceeded, however, and the body was warmed by the morning sun, small numbers of green bottle flies (Phaenicia sericata) were observed feeding at the bullet wound. By the time the corpse was removed from the scene, patches of eggs were present in and around the wound. Knowing that the previous day's climatic conditions were ideal for blow fly activity, that adult blow flies are not typically active at night, and that blow flies would be highly attracted to the pooled blood, entomologists concluded that the victim had been killed during the hours of darkness preceding the discovery of the body. It was later determined that the young woman had been last seen alive around midnight of the previous day.
THE IMPORTANCE OF BLOW FLIES: EGGS
Blow fly eggs, collected from remains and analyzed, can provide investigators with an accurate estimate of postmortem interval and allow them to focus more narrowly their investigative efforts.
Blow fly eggs are small (2 to 3 mm), whitish-yellow, and somewhat elongate. During warmer seasons they are frequently packed into natural body openings and wound sites and in large numbers are easily visible to the naked eye. In temperate areas during colder months, however, their numbers may be few, and they may be difficult to locate, being more deeply recessed in cryptic locations. Blow fly eggs will typically hatch within one to three days depending on species and environmental conditions. Dissection of egg samples and analysis of the state of embryonic development may further delineate the time since oviposition and, therefore, the time of the victim's death.
Case No. 4
On a midmorning in August, the half-nude body of a young female was discovered, more or less face down, among a group of junk automobiles near Spokane, Washington. The victim had died of multiple stab wounds to the chest and neck, and adult blow flies were observed in and around the wounds. Blow fly eggs were collected from the wounds at autopsy in the late afternoon. Subsequent dissection of the eggs showed no embryonic development suggesting that they had been deposited on the remains less than eight hours earlier.
The victim had been last seen alive during the evening two days prior to her discovery. The insect evidence, however, suggested that the young woman had been murdered during the hours of darkness preceding the finding of her remains. Had the victim died any earlier, young fly larvae (maggots) rather than eggs would have been collected from her wounds. Climatic conditions on both days prior to her discovery were suitable for adult blow fly activity and egg laying. A subsequent investigation verified these findings, revealing that the victim had been murdered during the hours of darkness just prior to the morning of her discovery.
Case No. 5
In early Spring, the fully-clothed body of a young, white male was found in a sandy, shrub habitat, in the southwestern United States. The victim had died of multiple small caliber bullet wounds to the chest and back. There was little external evidence of decomposition. A small amount of blood was observed to have oozed from the victim's left nostril, partially coating his left eye.
A small irregular granular mass was collected from the surface of the victimÕs left eye. Closer examination of this substance revealed it to be a small mass of blow fly eggs. Several eggs had hatched already.
These maggots were reared to adults and were subsequently identified as Cochliomyia macellaria, the secondary screw worm. Based on the climatic conditions and knowledge of the developmental biology of this fly, it was determined that the eggs most likely had been laid on the corpse 24 to 36 hours prior to the time the corpse was found. Subsequent investigation determined the identity of the victim. He had last been seen alive in the company of a male companion approximately 36 hours prior to the time his corpse was found. It was later determined that the victim had been murdered by his companion approximately 36 hours prior to discovery of the remains.
THE IMPORTANCE OF BLOW FLIES: MAGGOTS
Maggots grow rapidly, passing through three growth steps (instars) punctuated by moults before becoming fully grown. Typically, large numbers of larvae hatch together and move around the corpse as a group. In doing so, they disseminate bacteria and secrete enzymes which enable them to consume virtually all of the soft tissues of the corpse. Their growth takes several days to several weeks depending upon species, environmental conditions, and the number of larvae present.
Case No. 6
In November a partially clad woman's body was found by passing motorists in a wooded area approximately 50 feet from a well-traveled highway in suburban Washington, DC. The deceased was a young, adult black female, weighing approximately 116 pounds. Her body was cold, rigor mortis was absent, and only minor external decompositional changes were evident. The victim had died of multiple stab wounds to the chest and neck. During the autopsy, several large maggots were observed migrating away from the corpse. This behavior is characteristic of fully developed, post-feeding blow fly larvae. Several additional maggots were removed from the neck wounds and clothing.
The victim was subsequently identified as a 21 year-old mother who resided with her infant and parents in an urban apartment complex in southeast Washington, DC. She had been reported missing by her parents 18 days prior to the discovery of her body. She was last seen alive during the early morning hours on Wednesday, 26 October in the apartment of the primary suspect, who had a history of sex-related offenses and violent crimes and had recently been released from prison.
Witnesses recalled having seen a man and woman struggling and having heard a woman screaming in the vicinity of the apartment house during the early morning hours 18 days prior to her discovery. Hair from the victim's head and pubes was found on bed sheets in the suspect's apartment. A shoe belonging to the deceased was subsequently found in a secluded urban woodlot located a short distance away. Samples of blood and hair taken from the suspect's car also were identified as belonging to the victim. An analysis of auto carpet fibers, removed from the victim's clothing, further demonstrated that she had been transported in the same vehicle.
While considerable circumstantial evidence pointed to the suspect, an accurate estimate of the time of death was critical in establishing the sequence of events surrounding the death. Several conflicting estimates of postmortem interval, varying from 2 to 8 days, were offered by medical examiners and case investigators, based primarily on the physical appearance of the body and the extent to which autolytic changes had occurred within various organs.
The maggots observed in and around the body during the autopsy were identified. Rearing of maggots to the adult stage was not possible as none of the specimens had been maintained alive. Soil samples yielded no additional specimens. Numerous photographs depicting the crime scene, the surrounding vegetation and terrain, and the body itself were examined.
Climatological data, including maximum and minimum temperature, cloud cover, rainfall, wind speed and direction, and relative humidity were obtained from a National Weather Service (NWS) observatory located less than a quarter of a mile from where the victim's body was found. Additionally, reports describing the condition of the body when found and detailing autopsy procedures and results were reviewed.
The largest fly larvae inhabiting the remains were fully engorged third instar larvae and post-feeding larvae of Calliphora vicina. One specimen showed morphological signs of pupariation.
Based on the temperature records for the relevant period, the number of days necessary for Calliphora vicina to develop from egg to prepupa was calculated. Because the average daily temperature to which the developing flies were exposed was cool (10C) and because two few larvae were present within the corpse to elevate microenvironmental temperature, the postmortem interval was estimated to be 15 days.
Based on the entomological data and the other evidence acquired during the police investigation, the suspect was arrested and charged with first degree murder, kidnapping, and felony rape. He was eventually tried, found guilty of all charges, and was sentenced to a lengthy prison term. Later it was learned that he had murdered the victim during the early morning 18 days prior to discovery and had hidden the body, by covering it with tree branches, a mattress, and other debris, in a nearby urban woodlot. Three days later, again during the early morning hours, he had transported the corpse to the location where it was found. The materials used to hide the body may have prevented oviposition by adult Calliphora vicina during the first few days following death. The fifteen day postmortem interval was valid.
Case No. 7
The semi-nude remains of a white male were discovered under a bridge in southern Indiana during the second week of December. The remains showed little decomposition, with only slight skin slippage on the arms and upper torso. A considerable portion of the decendent's face (left side) was skeletonized, postmortem damage caused by rodent feeding. A few calliphorid larvae (Calliphora vomitoria) were found in the exposed sinus and oral cavities of the face.
The remains appeared to have been exposed only a relatively short period of time based upon the physical appearance. In this case, cool temperatures associated with the particular season of the year were important in estimating the approximate time of death. For southern Indiana, temperatures were below average in October, above average in November, and above average in December. Analysis of the blow fly larva development and comparison with climatological data suggested that it would take at least 48 days at the recorded daily maximum and minimum temperatures for the maggots to reach the size and stage found on the remains. When the investigation was completed and the remains identified, it was found that the decedent had wandered away from a mental institution 54 days prior to the discovery of the corpse. The decedent had died from hypothermia and exposure during an October night when temperatures fell well below freezing (24F).
Case No. 8
In the southeastern United States during mid-November, police were called to investigate a foul smelling odor which was emanating from a small single family home in an impoverished section of town. Investigating officers soon discovered the badly decomposed body of a young, black female in a shallow grave in the dirt basement of the dwelling.
The victim had died of a single bullet wound to the head inflicted with a small caliber rifle. Subsequently, a careful examination of the corpse and a detailed excavation of the soil in and around the grave site revealed the presence of numerous larvae of Calliphora vicina and larvae and pupae of a relative of the house fly, Synthesiomyia nudesita.
Specimens collected from the scene were reared in the laboratory. Supplemental information including climatic data and soil temperatures were reviewed in an effort to determine the intervening climatic conditions. Using information on the developmental biology of both of these species of flies, an estimate was made that the victim had died and was colonized by flies approximately 28 days prior to the time of discovery.
Investigators were able to target their investigation in and around the estimated time of death. Shortly thereafter a suspect was identified. This individual eventually confessed to having killed the victim 28 days prior to the time the body was found. She had attempted to bury the victim in a shallow grave located in the basement of the house shortly after committing the homicide.
In this case, larvae of multiple species of flies provided investigators with the only scientifically reliable method of estimating the time of the victim's death.
Case No. 9
Similarly, in early summer, the body of a young, unidentified, white female was found at the end of a logging road in a rural section of the northeastern United States. Investigation revealed that the unidentified young woman had died from a single shotgun blast to the right side of the head. While processing the crime scene, investigators collected representative samples of blow fly adults and maggots infesting the gaping wound.
These specimens proved to be mature larvae and adults of the black blow fly (Phormia regina). Following an in-depth review of climatic conditions, habitat characteristics, and crime scene photographs, entomologists estimated that the young woman had been killed about five days prior to her discovery and that her body had been placed in that location close to the time of her death.
Based in part on the entomological analysis, investigators circulated requests for reports of missing persons fitting the deceased description who had disappeared five days prior to the corpse discovery. Eventually, the young woman was identified and her boyfriend became the prime suspect. Just prior to his arrest, however, he was found hanged in a motel. A suicide note revealed that he had murdered the victim five days before her remains were found and had committed the homicide at the end of the logging road where she was discovered.
Case No. 10
On 26 August, a 37-year old black male was found in Kawainui Marsh, a swamp located approximately 1.6 km from the ocean on the windward side of the island of Oahu, Hawaii. The elevation for the site was only slightly above sea level. The body, clothed in blue jeans and a t-shirt, had a gunshot wound to the right frontal skull.
The corpse was in an advanced state of decay. The skull was largely devoid of flesh, although some was present on the lateral surfaces and the ears were relatively intact. The cervical area was largely devoid of flesh and the vertebrae were clearly visible. The groin area was largely decomposed and contained a large number of Diptera larvae. On autopsy, no penetration of the abdominal cavity by larvae was observed. Collections of insects from the remains yielded 2 species of Calliphoridae larvae. Chrysomya megacephala was represented by 3rd instar larvae from the chest, groin, and legs, while Chrysomya rufifacies was represented by 2nd instar larvae and 3rd instar larvae from the chest. None of the larvae from either species were in the prepuparial stage.
Temperature data were obtained from the nearest weather station, and climatic information from this station was analyzed for the time period in question. This analysis, when coupled with the developmental stages of the specimens collected, suggested a minimum postmortem interval of approximately 117 hours.
A subsequent investigation revealed that the decedent had last been seen at about 6:00 p.m. on 21 August when he departed for work. He failed to arrive at work as scheduled at 8:00 p.m. His remains were discovered on 26 August and were placed into a refrigerated crypt. This species Crufifacies does not form dense maggot masses, activity for this species would have ceased shortly after the remains were placed into the refrigerated crypt. The postmortem interval based on insect age in this case was about 117 hours and fit well with the last sighting of the decedent, and his failure to report for work.
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