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January 31, 1995

DEFENSE ATTORNEY JOHNNIE COCHRAN JR.: These are, as you know, already these are minute specks of blood. They may be saliva, they may be skin cells, dandruff, as I indicated to you, even a spray of a sneeze can contaminate the forensic sample. So what I want to do in this example, and we have these charts, here is this, in comparing the medical research, we compare the medical research with the forensic and see which one is more likely to be reliable under the circumstances. Well I think that we can, the evidence will show, that as opposed to the clean samples and the dirty samples, in this instance, the clean samples in the medical lab are far more reliable.... The next area we’ll be talking about is in a, generally, in a medical lab, you have a generous sample size.

The doctor can have whatever sample size he usually wants or needs. In forensics, the samples come, generally, in very, very limited, minute amounts. They’re working with such small amounts, often the test can only be done once. And, of course, we think the evidence will show that it is harder to produce reliable results under those circumstances. In fact, you will hear, I’m taking this case, that most of the important DNA tests performed by the prosecution was done with amounts of DNA that were actually below the preferred amounts for reliable testing. So, if you talk about the medical research labs having a generous sample size, and then in the forensics area having minuscule sample sizes, again, you can see there is a higher risk of contamination in the minuscule sample size.

That brings us down to the unmixed samples from known sources. As you know, and Ms. Clark alluded to this in her statement, in a medical setting, you have people that you know. If you have a lady who’s going to have an amniosynthesis (sic), you know who that is. If you have someone who’s going to give, one person’s going to give somebody else a kidney, you know who they are. So you have known sources that you’re dealing with. And that makes a big difference, as I think you’ll see during the course of the testimony. In medical testing, we take these unmixed samples from known persons.

In forensics, we use and collect samples that could be mixtures in varying amounts from a number of unknown people because you don’t know who’s been out there, who’s walked, who’s sneezed, who’s bled, who’s scratched their head. We don’t know over a period of time. We expect that you’ll hear, again, in this area, that the new forms of DNA testing used by the prosecution in this case, are just not reliable enough to use when analyzing mixtures from unknown sources,and the key thing here being with mixed samples from unknown sources.

So, again, once again on forensics,in the higher risk of contamination. Then in the lab, in the medical research area,there is generally minimal handling. This is fairly clear and straight forward. The less handling than at the scene, when you have someone going out, trying to collect something. Contrary, as I said, to what the prosecutor told you last week, the evidence will be it’s not as simple as wiping up a spill in your kitchen. This technology is so sensitive, it’s not that simple at all. You and I just shouldn’t go out and do this. We can do it, if we wanted to use the same techniques they’re using at the LAPD, but you get results that are all unreliable. So, between minimal handling and multiple handling, you can see again, there’s a higher risk of contamination with the multiple handling.

Errors rates, better known. And that’s because, I think you’ll hear testimony, that in the medical labs, they subject their results and things to tests. I mentioned the wipe test. In labs they do that because they’re concerned about contamination in the labs when you go to the doctor. You want to have the doctor make sure his lab is as contamination free as near as possible.


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