The “Making a Murderer” Case: A Brief Description on How EDTA Is Measured in Blood

In 2007, Steven Avery was sentenced to prison for the murder of Teresa Halbach. What made this case stand out was that Avery had recently been released from prison, after wrongfully spending 18 years incarcerated on a rape charge. Advances in DNA analysis were used to prove Avery’s innocence, resulting in his release. Avery quickly filed a lawsuit against Manitowoc County and former officials, whom Avery believed had framed him. In the midst of these procedures, Avery was again arrested for murdering Halbach. His nephew, Brendan Dassey, was also arrested and convicted as an accomplice. The handling of the Halbachmurder case was highly controversial. Steven Avery and his lawyers argued that they had he had once again been “set up” by his judicial adversaries. One central piece of evidence incriminating Avery was the presence of his blood at the crime scene. Avery’s attorney’s argued that the blood had been planted, arguing that the source was a test tube containing Avery’s blood, which local police forces had access to. But how determine if the crime scene blood was from a sample tube? The Avery tube contained ethylenediamine-tetraacetic acid (EDTA), which prevents blood coagulation and degradation. EDTA is not naturally present in human blood, and the defense argued that if EDTA was found in the crime scene blood, it would prove the blood was planted. The results of this analysis has generated vast discussion on social media and elsewhere, particularly following the documentary Making a Murderer1, which describes the life and trials of the Avery family. However, tools of forensics and chemical analysis are often “black boxes” to non-scientists, and perhaps early-stage science students as well. Even for the most curious and inquisitive, it can be difficult to learn more about these techniques, as they are mostly described in often-expensive scientific papers. Therefore, we would like to here describe the central technique used for determining EDTA in blood spots in the Avery case, namely liquid chromatography-mass spectrometry (LC-MS). We here attempt to describe it in relatively simple terms. Please note that we will not discuss the judicial aspects of the case, but merely describe a central scientific technique used in a trial that has captivated and concerned millions of people.