Friday, January 8, 2016
Several readers have asked me questions about the ethylenediaminetetraacetic acid (EDTA) evidence used in the Steven Avery/"Making a Murderer" case. This is an introductory post, which will focus upon the use of this evidence at Avery's trial.
This all comes from the Brief of Plaintiff-Respondent (the State of Wisconsin) in State v. Avery, 2010 WL 4736754 (Wis.App. II Dist. 2010). In 2005, Teresa Halbach was murdered. Apparently, blood that matched Steven Avery's DNA profile was found in the cargo and ignition areas of Halbach's vehicle. "Avery's defense at trial was 'that police officers who had access to a vial containing Steven Avery's blood, which was located in the clerk of court's office, planted Steven's blood in Ms. Halbach's car...."
According to the State,
The coup de grâce to the blood-planting theory was delivered by Dr. Marc LeBeau, who is the unit chief of the Chemistry Unit at the Federal Bureau of Investigation Laboratory in Quantico, Virginia (321:73). Dr. LeBeau testified that blood collection tubes typically contain a preservative or anticoagulant agent (321:90-91). The type of agent is indicated by the color of the tube's stopper (321:91). Purple-stoppered blood collection tubes use ethylenediaminetetraacetic acid (EDTA) as the anticoagulant agent (id.). Avery's blood was in a purple-stoppered tube (321:94).
Dr. LeBeau testified that the FBI laboratory tested a number of items of evidence for the presence of EDTA, including swabs taken from the bloodstains in Ms. Halbach's RAV4, control swabs taken from areas near the bloodstains, and Avery's blood from the purple-stoppered tube (321:94-99, 103, 114). The testing protocol used by the FBI was able to detect the presence of EDTA in a sample as small as one microliter of EDTA preserved blood, a minute amount equivalent to about one-fiftieth of a drop (321:129).
According to Dr. LeBeau, if the bloodstain swabs from Ms. Halbach's vehicle tested positive for EDTA and the control swabs tested negative, that would be an indication that the blood came from a purple-stoppered tube and had been planted (321:127). On the other hand, if EDTA were not found on the bloodstain swabs, that would suggest that the blood came from active bleeding and not from an EDTA-preserved tube (id.).
Dr. LeBeau testified that the FBI Laboratory was unable to identify any presence of EDTA in the bloodstain swabs or the control swabs from Ms. Halbach's vehicle (321:133-34). The blood from the tube containing Avery's blood, in contrast, contained “significant amounts of EDTA in it” (321:134). Dr. LeBeau testified, to a reasonable degree of scientific certainty, “that the bloodstains that were collected from the RAV4 could not have come from the EDTA tube” (321:135).
So, that's the State's position. (1) Purple-stoppered blood collection tubes use EDTA to preserved blood; (2) Avery's blood sample was in a purple-stopped blood collection tube; (3) Avery's blood sample had "significant amounts of EDTA in it;" and (4) the FBI Laboratory was unable to identify any presence of EDTA in the bloodstain swabs or the control swabs from Ms. Halbach's vehicle. Therefore, to a reasonable degree of scientific certainty, “the bloodstains that were collected from the RAV4 could not have come from the EDTA tube."
the defense called Janine Arvizu, an independent contractor who works as a laboratory quality auditor (324:5-6). Ms. Arvizu agreed that when the FBI's testing protocol produces a positive result, that is a valid indication that there is EDTA in the sample (324:23). She also testified that if the result were negative, she could not tell whether that meant that there was no EDTA or that the level of EDTA was below the testing method's detection limit (324:23-24). In Ms. Arvizu's opinion, it was “quite plausible” that the bloodstains swabbed from the RAV4 contained EDTA, “but the lab simply was not able to detect it” (324:59). However, Ms. Arvizu did not testify that EDTA was present in the swabs. Nor did she explain why, if Avery's blood vial was the source of the bloodstains in the vehicle, the EDTA levels in those bloodstains would have been below the FBI's detection limit given the FBI's finding that the blood in the vial contained significant amounts of EDTA (324:5-104).
So, that's the defense position. A "positive" FBI test is a valid indication that there is EDTA in a sample, but a "negative" FBI test does not necessarily mean that there is no EDTA in the sample because the level of EDTA could simply be "below the testing method's detection limit."
Those are the basic facts, at least as presented by the State of Wisconsin. This leaves the question of the reliability and EDTA testing. In future posts, I will address how EDTA testing has been treated by the courts, the FBI, etc.