 As evidence they offered the blood contained EDTA, a preservative found in purple top tubes used for blood draws, it was collected several weeks later on July 3, rather than on June 13, and 1.5 mL of Simpsons donated reference blood was unaccounted for.The officer who planted it was not named by the defense.The prosecution countered that the EDTA levels found in the blood was consistent with that found normally in unpreserved blood and not even close to the levels found in blood preserved in a purple top tube.