As any true crime purveyor (or Netflix-binge-watcher) knows, the murder of Kathleen Peterson has become an enigma over the past two decades. On December 9, 2001, her husband, Michael Peterson, found her unconscious at the bottom of the stairs of their mansion. Peterson was subsequently charged and convicted of his wife’s murder and sentenced to life imprisonment without the possibility of parole. The case, however, was far from over. Following a lengthy appellate process and scheduled retrial, Peterson was eventually released from prison in 2017 after entering into an Alford plea, during which he admitted the existence of evidence against him while maintaining his innocence. Over a decade of appeals (and a roving camera crew) later, the trials and tribulations, as well as the strengths and weaknesses of the case, have been exposed for public consumption in the Netflix miniseries, The Staircase.
Remarkably, Peterson’s (somewhat) exonerated ending stems from the faulty testimony of a self-described blood spatter expert. The Staircase not only examines how this particular expert shaped the (arguably) wrongful conviction of Peterson, but it also exposes the greater issue of expert unreliability in the forensic sciences and the implications of entrusting an accused’s fate to perception-based expert testimony.
The Facts of the Case According to the Blood Spatter Expert
Duane Deaver, the North Carolina State Bureau of Investigation agent and blood spatter analyst that examined the murder of Kathleen Peterson, is as ubiquitous a name to the documentary as the murder victim and accused. At Michael Peterson’s trial, Deaver testified that Kathleen died from being beaten to death and that the blood spatter patterns found on the stairwell walls and on Michael and Kathleen’s clothes proved that Michael killed her by bludgeoning her with a blunt object, namely, a blow poke. Contrastingly, the defense argued that Kathleen died by accidentally falling down the stairs. As part of Deaver’s qualifications as an expert, he testified that he participated in 500 cases involving bloodstain pattern analysis and had written 200 reports throughout his career. He also testified that he had personally investigated 15 crime scenes which involved falls. On this basis, Deaver was qualified as an expert witness in bloodstain pattern analysis. Deaver was considered to be a key prosecution witness and partly responsible for the guilty verdict that resulted in life imprisonment for Michael Peterson.
However, Deaver’s testimony was eventually called into question after he was fired by the State Bureau of Investigation for misrepresenting evidence in other major trials. During a 2010 innocence hearing for a later exonerated defendant in another case, Deaver stated that the State Bureau of Investigation had been consistently withholding blood evidence from defense attorneys on numerous occasions and he was only following their policy. It was then discovered that North Carolina’s State Bureau of Investigation had withheld or misrepresented evidence in over 200 cases. It was also revealed that Deaver grossly falsified his qualifications during his testimony, as his experience was much more limited than what he had represented to the jury. These groundbreaking discoveries formed the basis of Michael Peterson’s appeal.
In 2011, the Court held that Peterson was entitled to a new trial on the grounds that Deaver misled the jury and provided false and misleading testimony which was material to the case. Set for a retrial, Michael Peterson elected to enter into an Alford plea by which he was essentially sentenced to time served.
While the trial of Michael Peterson had finally come to a cinematic close, it also brought forth more questions concerning the legitimacy of a science that had previously been responsible for innumerous convictions.
Bloodstain Pattern Analysis: Reliable Evidence or Faulty Science?
The Peterson case has been one of the most publicized examples of unreliable and faulty blood spatter experts, however, the discipline of bloodstain pattern analysis as a whole continues to be scrutinized within the forensic science communities. But what exactly is bloodstain pattern analysis? Is it a legitimate science? And if so, how does one become an expert in the field?
Bloodstain pattern analysis refers to the physics of blood and the visual pattern recognitions that are found at a crime scene. Through blood spatter, an event can be reconstructed and information concerning the type of incident (murder, suicide, accident, etc.) can be ascertained. Principles of physics, such as gravity, liquid movement, and air resistance, are applied to bloodstain pattern analysis. The overall purpose is to define the facts surrounding an incident in question based on the specific patterns and flow of blood left at the scene.
Although there was some experimentation in the field of blood spatter dating back hundreds of years, the first significant expert testimony concerning this obscure science occurred in the 1955 case, Ohio v. Sheppard. The defendant, on trial for the murder of his wife, was found guilty then eventually exonerated at his retrial in 1966 in large part due to the testimony of Dr. Paul Kirk. Using blood velocity and angle impact data, Dr. Kirk testified that the murderer used his left hand to bludgeon the victim. The defendant notably suffered from a motor-sensory in his left arm. Dr. Kirk later developed a research project concerning the case.
Around the time of the Sheppard case, bloodstain pattern analysis began to pick up steam in the mainstream sciences and in the courtroom. In the 1957 precedential case, People v. Carter, the Supreme Court of California affirmed that bloodstain pattern analysis is an appropriate field of expertise and that Dr. Kirk qualified as an expert in this area. In this case, Dr. Kirk (who was testifying for the prosecution) performed an experiment involving sponge rubber, and a plastic sheet, and involved beating a wooden contraption to conclude how far away the murderer had to have been from the victim. Although affirmed as an expert, Supreme Court Justice Jesse W. Carter notably dissented in part, commenting that, “It most certainly cannot be said that an object made of wood, sponge rubber and a plastic sheet constitutes the same thing as a human head.”
In 1971, after receiving a grant from the Law Enforcement Assistance Administration, Herbert Leon MacDonell published Flight Characteristics and Stain Patterns of Human Blood, followed by his Laboratory Manual on the Geometric Interpretation of Human Bloodstain Evidence in 1973. He then created a training program for bloodstain pattern interpretation at the first bloodstain institute in Jackson, Mississippi and trained over 1,000 analysts in the field. In 1983, the International Association of Bloodstain Pattern Analysis was formed, giving further legitimacy to this relatively new forensic science. Since then, a number of cases have hinged on blood spatter expert testimony, with numerous states holding that bloodstain pattern analysis is a legitimate science and can be the basis of expert’s opinion.
However, not all blood spatter analysts are experts. For example, in State v. Halake, the Tennessee Court of Criminal Appeals overturned a first-degree murder conviction on the basis that a police officer, who had never attended a full course in bloodstain pattern analysis, was improperly admitted as an expert.
Bloodstain pattern analysis has been met with some criticism that questions the reliability of the science. A 2009 study conducted by the National Academy of Sciences found serious deficiencies in the field of bloodstain pattern analysis concluding that generally, opinions on blood spatter “are more subjective than scientific.” The report stressed that experts analyzing blood patterns should have, at a minimum, “an understanding of applied mathematics, the physics of fluid transfer and the pathology of wounds.” As stated in the study, “extra care must be given to the way in which the analyses are presented in court. The uncertainties associated with bloodstain pattern analysis are enormous.” The study linked faulty forensics to wrongful convictions, finding a “potential danger of giving undue weight to evidence and testimony derived from imperfect testing and analysis.”
A follow-up to the 2009 study further explored of the forensic sciences generally, with obvious implications for bloodstain pattern analysis. The 2016 Report to the President: Forensic Science in Criminal Courts studied the reliability and validity of pattern-based forensic science methods, such as latent print analysis, firearms and tool marks, shoe and tire prints, and bite mark analysis. The study focused on the problem of perception and cognitive bias of the analyst. For example, the study found that fingerprint examiners can be influenced by the interpretations of other examiners. The authors of the study recommended that forensic scientists have minimal exposure to other evidence in crime scenes (such a confessions or eyewitness identifications) to minimize the potential for bias.
That is not to say that blood pattern analysis can never be accurate. Like any scientific testimony, the reliability of the expert’s methodology is critical. Unlike the infamous Duane Deaver, an expert’s testimony that is based on reliable methodology, unbiased analysis, and of course, the requisite professional qualifications, can hopefully avoid the unnecessary problems that plagued Peterson’s trial.