Hair of the dog?

Most of us are familiar with the use of human DNA profiling to help identify evidence left at crime scenes; but what about animal DNA? Rob Ogden takes a look at how forensic scientists are developing techniques to identify all kinds of biological evidence from animal sources and how this is helping to solve some of the UK’s most serious crimes.

DNA is found everywhere - within every cell and within every tissue of every animal and plant. It is found at crime scenes in saliva, blood, hair and skin and can be transferred simply by shaking hands. Modern technology allows forensic scientists to produce individual DNA profiles commonly used in human forensics, but analysis of animal DNA can also tell us a lot more, such as what species a sample came from and which ancestral line it belongs to.

Animal DNA forensics is concerned with identifying non-human biological material that may provide relevant evidence to an investigation. There are several ways that this can occur: where the animal is the perpetrator of an offence (e.g. a dog attack), where the animal is the victim of an offence such as physical abuse or illegal fighting, or where an animal is not directly involved in a crime, but its DNA is transferred between the suspect and the crime scene, victim or evidence. Each of these scenarios provides opportunities for forensic scientists to analyse animal DNA.

Scientists in LGC Forensics’ Animal DNA Unit use two key technologies to identify animal DNA: DNA profiling and DNA sequencing. In each case, DNA is first extracted from the sample and then amplified using a technique known as polymerase chain reaction (PCR). PCR amplification produces multiple copies of specific regions of DNA, rather like photocopying a single page from a book. When a sufficient number of copies are produced, the DNA region is analysed to determine the specific genetic code (DNA sequencing) or to measure differences in the length of DNA fragments (DNA profiling).

Animal DNA profiling is used just like human DNA profiling, allowing the forensic scientists to match samples back to individual donors, or to understand the family relationships among a group of animals. The technique targets DNA held within the cell nucleus (nuclear DNA) which is present in two copies, one inherited from each parent. This is ideal for parentage investigation, but as the amount of nuclear DNA in a cell is limited, there is sometimes insufficient genetic material in a crime sample to generate a profile. Currently, LGC Forensics can apply DNA profiling to all UK dogs, and we would expect to see matching profiles in two different animals less than one in a billion times. For intelligence purposes, it is also possible to assess the most likely breed of dog that a DNA sample came from. In future, similar techniques are planned for cats.

DNA sequencing is used to identify the species of animal that contributed to the

evidence. By analysing genes that show differences from one species to another, an evidence sample can be assigned to its species origin with an extremely high level of confidence. Such species diagnostic gene regions are usually found in mitochondrial DNA, which is found in the mitochondria of every cell, outside the nucleus. A single cell may contain many thousands of mitochondria, therefore there is typically much more DNA available for analysis. This means that it is usually easier to obtain a species identification than an individual profile, allowing the analysis of trace evidence samples such as hair fragments.

For dogs, the DNA sequencing technique can be taken one step further to examine the ancestral line that a dog belongs to. This technique is less powerful than DNA profiling, but still allows individual samples to be compared and matched to support an investigation.

Animal DNA represents a new type of evidence and the potential applications are very wide-ranging. Even where animals are not directly involved in the crime, the transfer of animal DNA through the attachment of pet hairs or saliva to clothing or a vehicle allows a chain of evidence to be built up, telling the story of the crime. In the past few years, these methods have been used to identify animal species, lineages and individuals in support of many different investigations. Examples of where animal DNA has been used include:

• matching animal hair on a rape victim to those recovered from the suspect’s vehicle (species identification)
• excluding a police dog from causing bite marks following a dog attack (individual DNA profiling)
• matching animal hair fragments on a firearm to the owner’s pet (dog lineage analysis)
• matching canine saliva recovered from a murder victim to an attack dog (individual DNA profiling)
• identifying animal faecal samples from footwear (species identification)
• identifying dogs used in illegal dog fighting

As a novel sample type, animal DNA also has the potential to generate new evidence in cold case reviews as well as to open more avenues of investigation for current forensic casework. In the UK, where LGC Forensics is the only dedicated provider of Animal DNA analysis, police and other enforcement authorities are becoming increasingly aware of the emerging animal DNA technologies and the imaginative ways in which these can be used to help solve crimes.

In 2009, police investigated a murder committed in South London, in which a dog was used to attack and immobilise a 17 year-old victim before he was stabbed to death by the dog’s owner. During the attack, the dog was also stabbed, which left a trail of blood from the crime scene through the local housing estate, to the home of one of the suspect’s associates. Forensic scientists were able to recover a dog DNA profile from saliva on the victim’s clothing which matched the DNA profile from the blood trail and the profile of the suspect’s dog. The canine DNA evidence was crucial in piecing together the events around the murder, leading to a guilty verdict and a minimum sentence of 24 years in prison for the defendant.

The Royal Society for the Prevention of Cruelty to Animals (RSPCA) brings prosecutions in cases of animal abuse or mistreatment. Following an extensive investigation into illegal dog fighting in 2004, which included seizing dogs and raiding premises containing fighting pits, the RSPCA turned to animal forensics to provide evidence at the subsequent trials. Scientists were able to identify dog blood splatter on a wide range of evidence items, from doors used to build the pits, through to ‘breaking’ sticks used to unlock the dogs’ jaws. In addition, the individual DNA profile of a dog kept in Oxfordshire was matched to a fighting pit on Merseyside, demonstrating the organised nature of dog-fighting around the UK and ensured custodial sentences for many of those found guilty of persecution.

LGC Forensics has recently established the UK’s only dedicated Animal DNA unit to provide forensic analysis of non-human samples. The analysis of animal DNA links human DNA analysis with other biological identification services. For example, traditional identification techniques such as microscopy can now be supported by DNA analysis, to help in the identification of all kinds of biological evidence from animal hairs to insects. In this way, animal DNA analysis becomes an additional weapon in the forensic scientist’s armoury to help uncover the events surrounding crimes in the UK, from the serious, to the bizarre.