Forensics

by Val McDermid

  ‘Criminal cases are continually hinging upon this one point,’ he declares. ‘A man is suspected of a crime months perhaps after it has been committed. His linen or clothes are examined, and brownish stains discovered upon them. Are they blood stains, or mud stains, or rust stains, or fruit stains? That is a question which has puzzled many an expert, and why? Because there was no reliable test. Now we have the Sherlock Holmes’ test, and there will no longer be any difficulty.’

  The very title of Arthur Conan Doyle’s first novel, A Study in Scarlet, comes from Holmes’s lecture to Watson on the meaning of detective work. ‘There’s the scarlet thread of murder running through the colourless skein of life, and our duty is to unravel it, and isolate it, and expose every inch of it.’ When, shortly afterwards, the pair discover a ‘scarlet thread’ beginning in a lonely house off the Brixton Road, Watson is nearly sick at the scene, which seems frankly improbable given he’s a medical practitioner who has served in the Afghan Wars. But then, I am a writer whose work features blood and gore and yet I am squeamish about blood.

  But back to the book. A man has been stabbed in the side as he lay in bed and the blade has pierced his heart. ‘From under the door there curled a little red ribbon of blood, which had meandered across the passage and formed a little pool along the skirting at the other side.’ This time, there is no need for his new test; instead Holmes assimilates all the physical evidence in the house, and listens to a policeman’s take on the anonymous assassin. ‘He must have stayed in the room some little time after the murder, for we found bloodstained water in the basin, where he had washed his hands, and marks on the sheets where he had deliberately wiped his knife.’

  Reconstructing past events from blood found at a crime scene is known as Bloodstain Pattern Analysis. Conan Doyle’s imagination barely touched the edges of what spilled blood can tell modern experts. Two years before A Study in Scarlet was published, Eduard Piotrowski, an assistant at the Institute for Forensic Medicine in Poland, took the first steps in the discipline when he wrote a paper about interpreting bloodstains to explain the course of violent action itself, ‘Concerning the Origin, Shape, Direction and Distribution of the Bloodstains Following Head Wounds Caused by Blows’ (1895).

  Piotrowski put a live rabbit in front of a paper wall, smashed it over the head with a hammer, and got an artist to paint the gory result. The colour illustrations in the paper are as accurate as they are grisly. He battered other rabbits to death using rocks and hatchets, varying his position and angle of attack to see how it affected the shape and position of the bloodstains. We can’t know how he felt during the experiments, but in his paper he expressed a nobility of purpose: ‘It is of the highest importance to the field of forensic evidence to give the fullest attention to bloodstains found at the scene of a crime because they can throw light on a murder and provide an explanation for the essential moments of the incident.’

  Nevertheless, Piotrowski’s pioneering work gained little attention until the mid-twentieth century. In a key case in 1955 a handsome doctor named Samuel Sheppard was convicted of bludgeoning his pregnant wife to death in the bedroom of their home on the shore of Lake Erie in Ohio. He maintained that a ‘bushy-haired intruder’ had attacked his wife (and the back of his own neck, which was injured in a way that would have been extremely difficult to self-inflict).

  At his trial, and again at his retrial in 1966, forensic scientist Paul Kirk of the University of California, Berkeley, testified for the defence: ‘When a weapon hits a bloody head, the blood flies out like the spokes of a wheel, radially, in all directions.’ Kirk showed photographs to the court of a blank area on the wall to the side of the bed where the killer had stood and battered Mrs Sheppard. ‘It is entirely certain,’ he said, ‘that the murderer received blood on his person, and no portion of his clothing that was exposed could have been exempt from bloodstaining.’ When police had first arrived at the house Sheppard was shirtless and in a state of shock. The only bloodstain they found on him was on the knee of his trousers. He couldn’t remember how he had come to be shirtless: ‘Maybe the man I saw needed one. I don’t know.’ A torn t-shirt of Sheppard’s size was later found near the house, with no blood on it. Kirk’s convincing testimony at the retrial helped overturn Sheppard’s conviction. He walked free after eleven years in jail.

  From top left: Samuel Sheppard after the alleged attack, his wife Marilyn Reese Sheppard and Sheppard testifying at his trial in a neck brace. He served ten years of a sentence for second-degree murder; he was found not guilty at a second trial in 1966

  Five years later the US government published the first modern handbook on bloodstain analysis, Flight Characteristics and Stain Patterns of Human Blood (1971). The handbook, and its sixty colour photographs, showed CSIs that bloodstaining could reveal how and where a fatal blow was delivered, the kind of weapon used, the likely bloodstaining on the murderer, whether the murderer bled, too, whether they moved the victim post-mortem, or whether the victim themselves moved before dying.

  The police still use blood spatter analysis every day: to date, it has helped solve thousands of crimes. But the seismic change in the significance of bloodstains came in the 1980s with the discovery of genetic fingerprinting. The question of ‘who’ could now be added to the list of ‘what’, ‘where’ and ‘how’. Since the early twentieth century, scientists had been able to identify the blood type of a suspect from a sample of blood or semen. Though this was useful in narrowing down the pool of potential suspects, the frequency with which some blood types occur in the general population meant it could usually only be used as circumstantial evidence. Blood typing was a far cry from the forensic possibilities offered by DNA.

  For thirty-two years Val Tomlinson has been investigating bloodstains at murder scenes, and analysing DNA in laboratories, first with the British Forensic Science Service (FSS) from 1982 until it closed in 2011, and since then with LGC Forensics. She is a mild-mannered, genial woman whose appearance belies her intimate relationship with blood – the way it moves, its inner chemical structure, the messages it carries with it – and her profound understanding of the genetic codes that underpin every human life. ‘There is a logic to DNA. Scene work is more an art than a science, bizarrely.’

  Dr Paul Kirk examines blood spatter on Marilyn Sheppard’s pillow

  By the time Val arrives at a murder scene with a pad of blank paper under her arm, CSIs have usually photographed and videoed every square inch. ‘Many a time I’ve had a debate with the bobby on the door who goes, “Why are you drawing it, Ms Tomlinson? There’s no need.”’ But – like an artist painting a landscape – Val wants to completely immerse herself in the scene. ‘I can take 200 photographs on holiday and when I come home they’re just snapshots. But if I stand and draw the scene I’m drawn to specific aspects of it. Very slowly I build up a picture and eliminate irrelevant things. All of the items might be completely irrelevant except one and I can highlight that. A photograph just shows everything that’s on the table. There is no emphasis on, say, an item that’s turned over, a bloodstained item, a coffee mug.’

  Once Val has been in a scene ‘for five or six hours’ she has ordered it, made it logical. Thus the act of drawing is more important than the drawing itself. ‘Even if I haven’t got all the answers I can at least give a discourse about what I’ve seen and the possible sequence of events.’ She imparts this narrative to the Senior Investigating Officer and then later to the court, where she uses her scene drawings ‘probably just as much as photographs, because the jury can get hold of them, be taken away from all the things that might distract them in the room, and brought into what matters.’

  More than anything else at the crime scene, blood matters to Val. Like any other liquid, its dynamics are subject to the laws of physics. If it strikes a floor at right angles it produces a circular stain, often because it has dripped slowly from a person or object. If it travels at an angle it will produce an elliptical stain, usually caused by a punch or a blunt
weapon. The longer and thinner the ellipse the more acute the angle of impact. If a group of bloodstains on a surface radiate ‘like the spokes of a wheel’ they probably came from a blow (or blows) inflicted in one place. A blood spatter expert like Val can calculate the angle of impact of the stains, then attach a piece of string to each one and spool it back at the appropriate angle. The strings will converge at the point where the blow was made. So if, for example, the point of convergence is located close to the floor, the victim could not have been standing when they were struck. Photographs of this ‘stringing model’ can then be used in court. And, increasingly, angles of spatter impact can also be put into a computer program, such as ‘No More Strings’, to make a 3D model of blows given at a crime scene.

  Cause of death isn’t always a mystery: at a scene of battery or stabbing it can be pretty obvious, in which case the SIO might find Val’s analysis sheds more light on the incident than the pathologist’s post mortem. Is the blood spatter confined to one area, showing that the victim dropped immediately to the floor? Did he stay on his feet and put up a fight, in which case blood might have dripped down his clothes? Did the murderer drag the body for some reason, causing the hair to spread out backwards or the clothing to ruck up, perhaps spreading a trail of blood across the floor? Are the ankles crossed over, indicating that the body has been turned over? The answers to these questions can give the SIO useful information about the actions of the suspect and events surrounding the death of the victim.

  SIOs want Val to tell them as quickly as possible how bloodstained the suspect is likely to be. ‘The last one I went to, there was an awful lot of bloodstaining at an old Victorian house with lots of rooms. You could see the way the assailant had gone out because every doorway had smears of blood down where the clothing had touched it. Ultimately it turned out they’d burnt the clothing but that was recovered and it was still bloodstained.’

  The police are racing against the clock to find the suspect before they dispose of vital evidence. But bloodstaining – like much physical evidence – can be surprisingly hard to get rid of. Val is sometimes called away from the scene of crime to the home of a suspect to examine doors and clothes. ‘Often they’ve had a clean up, so we look at the contents of the washing machine.’ Forensic scientists don’t give up on evidence easily, something John Gardiner found out to his cost when he tried to dispose of vital evidence in the manslaughter of his wife in 2004 (see p.174).

  But blood analysts can’t always report so usefully, especially when they aren’t given five or six hours to form an artistic relationship with the crime scene. ‘I’ve heard horror stories of scientists going to scenes and being told, “I want you to look at the blood pattern over there and that’s it,”’ Val admits. ‘To me, that’s a disaster waiting to happen. We need to be part of the whole picture.’ In some cases analysts testify in court without having visited the scene at all, as a happened in a tragic and complicated case that began on 15 February 1997, in the coastal town of Hastings, East Sussex.

  In the late afternoon 13-year-old Billie-Jo was putting a lick of paint on the patio doors of her foster parents’ home. Siôn Jenkins, her foster father and deputy head of a nearby school, returned from a trip to a local DIY store with two of his own daughters. One girl walked round to the patio to talk to Billie-Jo, and let out a scream. Billie-Jo was lying on her front with her head caved in. Siôn pushed her shoulder up to get a better look at her face, and saw a bloody bubble appear at her nostril, which then popped. He called 999, and paramedics pronounced Billie-Jo dead at the scene.

  CSIs found a bloodied metal tent peg near the patio, measuring 46 cm by 1.5 cm. The autopsy showed that the attacker had inflicted at least ten ferocious blows to Billie-Jo’s skull. The following day a bloodstain analyst came to examine the scene and found radiating spatter on the wall next to the patio, the inner surface of the patio doors and the dining room floor.

  When a child dies in suspicious circumstances, the police often begin to look very carefully at those closest to them. Siôn Jenkins’ clothes and the tent peg were sent to the FSS for analysis. On 22 February scientists discovered 158 tiny blood spatters on his trousers, jacket and shoes – too small for the naked eye to see. Were the spatters there because Jenkins had battered his daughter? Or did Billie-Jo breathe a mist of blood on to him with her dying breath?

  A number of days after the murder the bloodstain analyst concluded that the blood on Jenkins’ clothes was consistent with him being the attacker, but couldn’t be certain there wasn’t another explanation.

  The police arrested Jenkins on 24 February and his trial began on 3 June. A scientist instructed by the prosecution had made bubbles with a blood-filled pipette and burst them next to a white surface. The ‘pop’ produced a fine spatter that travelled downwards and sideways up to 50 cm – but no spatter rose upwards. Next he filled a pig’s head with blood and beat it with the same type of tent peg found near Billie-Jo. This left a fine spatter on his overalls.

  A scientist instructed by the defence had done some of his own experiments. He put some of his own blood in his nose and exhaled over a white piece of paper an arm’s length away. He also found a fine spatter.

  The prosecution argued that Billie-Jo was already dead when Jenkins pushed her shoulder to see her, and so couldn’t have made a breath. Paediatrician David Southall testified, ‘Anybody approaching a child with an injury who is gasping would be in no doubt whatsoever that the child was breathing and still alive and would report that because it would be so obvious to an observer.’ However, neuroscientists had not reached a consensus on exactly when a brain was too injured to cause the respiratory system to produce one more breath. Pathologists for the defence thought that Billie-Jo could have survived long enough to exhale on to her foster father. Under cross-examination the two bloodstain analysts testifying as part of the defence case agreed that the spatter on Jenkins’ clothes may have come from the impact of the tent peg.

  Siôn Jenkins continued to protest his innocence, but was convicted of murder on 2 July 1998 and was sentenced to life imprisonment. Some rejoiced at the verdict. Others were shocked at how little evidence it was based on, believing that the police had relied too heavily on the assumption that the murderer was likely to come from within the family. In the previous two years there had been eighty-five reports of prowlers and suspicious characters near the Jenkins’ home in Hastings. The New Statesman railed at the conviction, claiming that ‘The police had a redhot suspect: someone with a psychiatric history and a known record of violence towards children, whom a number of people saw loitering nearby on the afternoon of the murder. When the police went to interview him he seemed strangely to have disposed of most of his clothing. Whoever the true murderer is, he now has the opportunity, as a result of the vagaries of British justice, to kill someone else’s daughter.’

  When Siôn Jenkins appealed against his conviction in 2004, the pathologist instructed by the defence presented new evidence about the state of Billie-Jo’s lungs. The original autopsy had found them to be hyperinflated, which meant that something (probably blood) was preventing some air escaping. The pathologist suggested that if the blockage was in the upper airways it could suddenly have been released and caused the spatter on his clothes whether Billie-Jo was dead or alive. Two retrials followed, both of which ended in the juries failing to reach a verdict, and, in 2006, Jenkins was acquitted. In July 2011 he got a PhD in Criminology from the University of Portsmouth. Now he works with pressure groups trying, among other things, to ensure that experts who appear in court are properly experienced and impartial. The real murderer of Billie-Jo Jenkins has never been found.

  In 1984, Alec Jeffreys was in his lab at the University of Leicester when he experienced a ‘eureka moment’. He had been checking X-rays of a DNA experiment comparing members of his technician’s family: looking at the results, it was immediately obvious that he had stumbled upon a technique which could reveal the unique variations in the DNA of any individu
al. Since this chance discovery, DNA profiling (or genetic fingerprinting, as it is sometimes called) has become the ‘gold standard’ of forensic science. When Sherlock Holmes dreamt up his test for haemoglobin he could proudly state, ‘It appears to act as well whether the blood is old or new. Had this test been invented, there are hundreds of men now walking the earth who would long ago have paid the penalty of their crimes.’ Within one hundred years of those words being published, real detectives would be able to know whose blood they had found at a crime scene. Such knowledge might indicate guilt or, just as importantly, make a compelling case for innocence. For example, if blood found at a rape scene does not belong to the victim or the suspect then, at the very least, you are looking for another person, someone who might have vital information – or who might be the real culprit. In the USA alone 314 people who were languishing in jail, some on Death Row, have been exonerated because of new DNA evidence.

  Genetic fingerprinting astonishes people even more than physical fingerprinting did at the turn of the nineteenth century. In the public imagination it stands triumphantly astride other physical evidence. Forensic scientist Angus Marshall remembers ‘a legendary case in the States where a jury came back to the judge and said, “We’re not going to accept blood splatter evidence, we want to see DNA.” They were practically dealing with a confession but they still didn’t believe it. It was ludicrous.’

  As this suggests, DNA profiling has not always been seen as a purely positive development. But when Alec Jeffreys was asked on the twenty-fifth anniversary of his discovery whether genetic fingerprinting was now being used in a way he was no longer proud of, he replied, ‘Catching large numbers of criminals, exonerating the innocent – some of whom have spent more than thirty years in jail – immigrant families reunited … I would argue the good heavily outweighs the bad.’