Animal evidence

DEFINITION: Organic materials from nonhumans, excluding insects, analyzed by forensic scientists for use in legal cases.

SIGNIFICANCE: With advancements in DNA fingerprinting of dogs, cats, and other domesticated and wild animals, animal evidence has become much more useful in criminal and civil court cases than it was in the past, when individual animals, breeds or even species could not be identified.

The animal evidence involved in cases of crimes against humans most often consists of shed hairs and traces of blood, other body fluids (including saliva and urine), and excrement from either dogs or cats. Given that in the United States about 40 percent of households include at least one dog and 30 percent include at least one cat, crime scene investigators frequently encounter this kind of evidence.

Animal Hair

In relation to crimes against humans, the most commonly analyzed type of animal evidence is shed hair. Research has shown that it is almost impossible for a person to enter a house where a dog or cat lives and not have some of the animal’s hair transferred to his or her skin, shoes, or clothing. Criminal perpetrators who live with dogs or cats can thus transfer the hair of their animals to victims or crime scenes. Perpetrators can also pick up animal hairs from crime scenes, from victims’ clothing, from household items, or directly from victims’ pets.

In 1994, white hairs from a cat named Snowball were used to help convict a Canadian man of murdering his wife. Police investigators found the hairs on the husband’s black leather jacket. This was the first evidentiary use of nonhuman DNA (deoxyribonucleic acid) to help solve a crime. In this case, the DNA analysis used feline microsatellite markers mapped by English geneticist Alec Jeffreys. Scientists have concluded that both feline and canine microsatellite markers are almost as discriminating as their human counterparts, not very much diminished by the inbreeding often seen in canines.

Because shed hair lacks a viable root, it usually does not contain enough nuclear DNA to allow short tandem repeat (STR, or microsatellite) fingerprinting of individuals. Instead, criminalists extract and amplify mitochondrial DNA (mtDNA) from the hair shaft, which contains thousands of mitochondria. This type of DNA identification of dogs and cats is most often used to add a layer of evidence rather than to provide a strong association to a particular animal, given that only a single locus is used for mtDNA profiling. In 2002, however, canine mtDNA was admitted into court during the prosecution of David Westerfield in the abduction and murder of seven-year-old Danielle van Dam, whose family owned a pet Weimaraner. This was the first trial in the U.S. to admit canine mtDNA analysis as evidence.

Forensic scientists also analyze the morphological (structural) characteristics of animal hair using compound light microscopy. Characteristic patterns of scales on the cuticle covering the shaft, for example, can be used to determine a particular species. Also, the medulla inside the shaft is informative for the identification of different species; for instance, the medullae of feline hairs show a typical “string of pearls” pattern. These features, among others, are usually used in conjunction with DNA profiling to identify particular animals.

Other Types of Animal Evidence

Animal blood found at crime scenes usually contains enough viable nuclear DNA for STR analysis, which can be used to identify an individual animal. As early as 1998, STRs obtained from dried canine blood linked a suspect to the murder of a Seattle couple and the killing of their dog. Although the suspect was convicted, the canine DNA evidence was not admitted at trial because canine DNA typing was not considered reliable at the time. Since then, the reliability of canine and feline STR profiling has been well established in the scientific literature, and dog and cat DNA evidence is regularly admitted in legal proceedings.

Both urine and excrement from dogs have also provided nuclear DNA to help solve crimes and convict criminals. One example of using DNA from animal fecal matter outside the legal justice system is the identification of the Canadian lynx from scat found near the large cat’s paw prints in snow. This technique is being investigated as a way to track the health, distribution, and population densities of certain endangered animal species.

The National Fish and Wildlife Forensics Laboratory in Ashland, Oregon, is dedicated to the collection and analysis of evidence of crimes against wildlife. Law-enforcement agencies submit to the lab the types of animal evidence discussed above in addition to more unusual samples, such as hunting trophies (antlers), carved ivory, hides, furs, bones, teeth, leather goods, feathers, claws, talons, whole carcasses, stomach contents, and Asian medicinals, among other organic and inorganic materials usually investigated in criminal cases. forensic experts at the facility extract and profile DNA from many of these items; they also employ other methodologies such as morphological and chemical analysis to determine whether samples come from particular species. Much of this work is concerned with supporting law-enforcement efforts to address crimes involving endangered species.

The emerging field of veterinary forensics is involved in identifying cases of animal abuse against domestic pets. In situations where abuse is suspected, veterinarians or veterinary pathologists most often obtain evidence from deceased whole animals, which are worked up in a manner similar to that employed during autopsies in homicide cases. These professionals look for specific patterns of injuries, telltale wounds, bullet holes, ballistic material, evidence of malnutrition or starvation, signs of torture, and incriminating human evidence (such as blood or hairs). Sometimes insects and maggots found on or in proximity to an animal carcass can be employed to determine the time of death or crime scene location.

During the twenty-first century, law enforcement agencies increasingly began utilizing animal forensic evidence in investigations regarding wildlife. This includes cases involving poaching, the exploitation of protected flora and fauna, and even illegal logging. In doing so, law enforcement agencies use animal evidence to aid in species preservation and conservation.

Bibliography

Cassidy, Brandt G., and Robert A. Gonzales. “DNA Testing in Animal Forensics.” Journal of Wildlife Management 69 (October, 2005): 1454-1462.

Cooper, John E., and Margaret E. Cooper. Introduction to Veterinary and Comparative Forensic Medicine. Ames, Iowa: Blackwell, 2007.

Cooper, John E., and Margaret E. Cooper. Wildlife Forensic Investigation: Principles and Practice. CRC Press, 2013.

Dorion, Robert B. J., ed. Bitemark Evidence. New York: Marcel Dekker, 2005.

Huffman, Jane E., and John R. Wallace. Wildlife Forensics: Methods and Applications. Wiley Blackwell, 2012.

Linacre, Adrian. "Animal Forensic Genetics." GENES, 1 Apr. 2021, doi: 10.3390/genes12040515. Accessed 13 Aug. 2024.

Merck, Melinda D. Veterinary Forensics: Animal Cruelty Investigations. 2nd ed, Wiley Blackwell, 2013.

Saferstein, Richard. Criminalistics: An Introduction to Forensic Science. 9th ed. Upper Saddle River, N.J.: Pearson Prentice Hall, 2007.

"The Importance of Forensic Science in Wildlife Investigations." UF Colleges of Medicine, Veterinary Medicine, and Pharmacy, online.forensics.med.ufl.edu/online-graduate-programs/certificate-programs/wildlife-forensic-sciences-and-conservation/the-importance-of-forensic-science-in-wildlife-investigations/. Accessed 13 Aug. 2024.