So back to the OP, lets assume there was EDTA and that the blood was not planted or cross-contaminated in the lab. Where could that EDTA have come from?
So you’re asking “If we remove all possible sources of EDTA, where did the EDTA come from?”
I remember during the trial that EDTA is in products like detergents so that EDTA contamination was possible without the police/lab. But with the information in this thread that doesn’t seem right. So my question is an honest one.
First I want to reply to yoyodyne’s post that precedes the above quoted post by Saint Cad. I am not sure who yoyodyne refers to, but if he refers to me, he is mistaken. I have always had a tentative leaning toward Roger Martz and Dr. Terry Lee’s theory regarding contamination by leftover residue. But yesterday I arrived at a firmer resolution. I now have a respectable degree of confidence in their theory. In regard to that I shall make another, longer post below. I may still reply to subsequent replies, but as far as my original question is concerned, I consider it answered and my next post should wrap up this thread.
Regarding my quote of Saint Cad here, there actually is a third possibility. As Marcia Clark explains in Without a Doubt, many substances use EDTA as a preservative. For example, detergent and foods. So, at least during the time of the criminal trial, there was a possibility that the EDTA in Nicole’s blood on the socks came from detergent. And there was a possibility that the EDTA in Simpson’s blood on the gate came from something he ate. Those sources are unlikely, however. As I intend to explain in my next post. 
I now have a reasonably confident answer to the question that started this thread. I arrived at it yesterday after pasting my above excerpts from Dr. Terry Lee’s testimony in the civil trial (see my above reply). FBI toxicologist Roger Martz and bio-molecular expert Dr. Lee were correct. Logic indicates that THERE WAS NO EDTA IN EITHER NICOLE’S BLOOD ON THE SOCKS OR SIMPSON’S BLOOD ON THE GATE. The EDTA came from the testing equipment.
Here is my information and rationale:
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During the criminal trial, Dr. Frederic Rieders was an expert witness for the defense. He explained that EDTA was not present in human blood. But lab tests done by the FBI, primarily those done by FBI toxicologist Roger Martz, indicated the presence of EDTA in two specimens of blood evidence. One was of Simpson’s blood, taken from the gate at the rear end of the walkway at Nicole’s condo (the crime scene). The other was of Nicole’s blood, taken from socks found in Simpson’s bedroom. (I presume those were Simpson’s socks.)
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Because it prevents blood from coagulating, EDTA is normally used as a blood preservative. When human blood is extracted, it is stored in purple-capped test tubes coated with EDTA. Therefore, as Dr. Rieders explained, since EDTA was found in the two specimens of evidence, there was a possibility the blood did not come from the bodies of Nicole and Simpson. Possibly it came from purple-capped test tubes. Which suggests that the blood had been planted.
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Roger Martz also took the stand. He firmly disbelieved that the blood had been planted. He presented a bar graph showing that the percent volume of EDTA in the two evidence samples was extremely less than the percent volume of EDTA in the blood a from purple-capped test tube. Therefore the blood evidence did not come from any purple-capped test tubes.
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For the criminal trial, the trouble was that the prosecution’s rebuttal of the EDTA/planting theory was complicated and obscure. In fact–someone please correct me if I’m wrong–Roger Martz never came right out and admitted that his tests detected EDTA, per se. He said his tests had found only molecules resembling the structure of EDTA. Dr. Rieders said that Martz’s tests did detect EDTA. Anyway, the jury was confused., and regarding the blood evidence, their minds had become doubtful.
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EDTA is found in many substances. On one webpage, I read a post where someone had seen EDTA listed as an ingredient on the side of a beverage container. I have also read that EDTA can be found in detergent and some foods. So, did the EDTA for the sock’s blood come from a detergent that had been used to wash the socks? Did the EDTA for the smear of Simpson’s blood on the gate come from something he had eaten or drank? My answer is no to both questions. The percentage of EDTA in the blood from socks and the gate was equal. That would not be the case if the EDTA had come from different sources.
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Puzzled by his findings, Roger Martz conducted two other tests for EDTA. He used a specimen of blood evidence from Nicole’s dress (it was Nicole’s blood), and a specimen of his own blood. He found EDTA in both, and the percent volume was again very small compared to that found in purple-capped test tubes.
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When Dr. Rieders was asked about the EDTA that Martz found in his own blood, he was very skeptical. Perhaps Martz’s lab technique was incompetent. Whatever the reason for Martz’s supposed finding, EDTA was not normally found in human blood, and Martz should not have found it in his own blood. So Dr. Rieders left room for the jurors to wonder if Roger Martz was part of a blood-planting conspiracy. Was Martz lying when he said he tested his own blood and found EDTA? Was he merely fabricating results from an imaginary test? More doubt was raised because digital records of Martz’s tests were deleted. (Deletions were normal procedure–computer memory was limited in those days–but the deletions caused more doubt.)
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Dr. Rieders was also asked why the percentage of EDTA was so small in the evidence specimens. He theorized that the EDTA had degraded after it was planted. He suggested that by the time Martz tested the evidence specimens, the amounts of EDTA in that blood had fallen greatly from the amounts each specimen had when it was in sealed purple-capped test tubes.
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Dr. Rieders theory of degradation made me doubtful regarding the blood from the gate. I could not believe that the multitude of blood specimens in the Simpson case could have been planted. That was ridiculous. But I did some reading on the Internet, and I discovered that EDTA could indeed be degraded by light. That troubled me. I knew that the blood evidence from the gate was collected under dubious circumstances. Though it had been observed by a number of persons and documented, Criminalist Dennis Fung forgot to collect it on the day after the killings. On July 3 prosecutor Bill Hodman saw the blood on the gate and asked about it. Only then was it processed. So twenty-one days passed before that blood evidence was collected. If there had been EDTA in it, plenty of time had passed for it to have been degraded by light, and maybe other environmental factors.
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But I was not lending enough weight to Dr. Lee’s testimony. Maybe I can be excused for that because Dr. Lee’s testimony was shallow and vague. On the stand he said, “And these evidence samples were – came from different places and were treated differently; yet they all show the same levels. And so it’s difficult to imagine the degradation that would be common to all the samples.”
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Today I understand that piece of testimony more fully. I understand why it solidly refutes the theories that the blood was planted and that the detected levels of EDTA were low because the EDTA degraded. Maybe I can be clearer than Dr. Lee was on the stand:
Four samples of tested blood are at issue here: blood from the gate, blood from the socks, blood from Nicole’s dress, and blood from Roger Martz’s own body. In each of them, Martz detected EDTA at low levels. Extremely lower than should have been detected if the blood was planted from purple-topped test tubes. Of course Martz’s own blood came from him, not from test tubes, but Dr. Rieders cast doubt on Martz’s unorthodox testing of his own blood. And maybe degradation could explain the low level of EDTA in the blood from the gate. Right?
Wrong. Here’s why: Not only did the four tests show low levels of EDTA, they showed equivalently low levels. Not precisely equivalent, but reasonably so. But if the EDTA in the gate’s blood came from food or drink, it would not be equal to the amount present in the sock from detergent. Nor would it be equal to the amount of EDTA in Martz’s own blood, however that EDTA got there (surely he did not swallow detergent). Maybe, if Simpson’s housemaid used the same brand of detergent to wash Simpson’s socks as Nicole used to wash her dress, the percentage of EDTA in the blood from the socks and from Nicole’s dress would be roughly equal. But they would not be equal to the amount of EDTA in the blood from Martz’s body or from the gate.
And Dr. Rieders must have been wrong regarding the degradation. After twenty-one days of exposure, it would be incredibly unlikely that the degraded EDTA from the gate would be at a level equal to that in the other three test samples.
So, neither degradation nor EDTA from environmental sources like detergents and foods can, with reasonable assurance, explain where that detected EDTA came from. Why were the levels detected during tests of those four samples equally low? At this moment, I see only one reasonable answer. The EDTA came from a common source, shared by all four samples. And that common source was the testing equipment. 
NOTE: This is basically the same conclusion presented in Daniel Petrocelli’s Triumph of Justice. But his presentation was not detailed. It did not resolve the doubts I had regarding Dr. Rieders’ theory of degradation. To resolve those doubts, I had to reexamine the evidence and do some thinking. 