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DNA Analysis and Maintaining Focus in an Extraordinary CaseRobin W. Cotton, Ph.D.
Participation in the case of the People of the State of California v. Orenthal James Simpson looked like a risky undertaking when Cellmark was first contacted regarding doing DNA analysis. The high profile nature of this case would almost certainly present extra non-scientific problems for the laboratory. Rather than address these problems as they arose, a team was assembled to anticipate case-related problems and plan in advance how to handle them. This team consisted of Cellmark Diagnostics' President, the person designated responsible for media relations, the Laboratory Director and the staff members doing the evidence analysis. During the laboratory's involvement in the case, non-scientific questions would be decided by the team and all scientific decisions would be made by the laboratory analyst and the Laboratory Director, including additional staff when appropriate. The team also decided that no special and/or additional procedures or record keeping would be used in the analysis of the evidence in the Simpson case. Several months before the initial receipt of evidence for the case, the laboratory had finalized and submitted its application for accreditation to the American Society of Crime Laboratory Directors/Laboratory Accreditation Board (ASCLD/LAB). Among other things, this application included detailed information regarding our laboratory protocols and our quality assurance program. All of these items had been thoroughly reviewed before submitting the application. The staff felt that all cases submitted to the laboratory are important and our procedures and record keeping methods sound. Therefore, no modifications specific for this case would be made. Eventually, there were minor modifications made to several non-scientific policies in response to orders from the Superior Court. We were least familiar with the handling of the news media. Shortly after the initial samples were submitted, our authorized contacts for the case were expanded to include the prosecutors and the Media Relations Director for the Los Angeles District Attorney's office, with whom we were allowed to discuss responses to media contacts. These discussions were not about details of the evidence analysis but rather about providing information about forensic DNA analysis in general. A policy emerged which was an extension of our experience prior to the Simpson case. The policy was as follows:
At the outset of the case, our confidentiality policy was reviewed with all Cellmark staff and brief meetings were held periodically in order to review this policy and to provide general information to keep everyone informed. Our policy regarding confidentiality is outlined as follows:
We suggested to the media relations director of the Los Angeles District Attorney's Office that we continue to provide general information about DNA identification to the news media while maintaining our normal policy to provide no case-related information. This policy was agreed upon; Cellmark continued to respond to media questions with general scientific information while maintaining case-specific confidentiality. Finally, the team reviewed security procedures at the laboratory. Additional outside security was hired for the period of time when the evidence was at Cellmark. After the evidence was returned to Los Angeles, we returned to our normal security procedures. Two additional policies which were already in place proved to be especially useful. These were policies for observation of case work analysis by outside experts and a standard method of handling discovery requests. These established policies eliminated the need to spend valuable time discussing these issues and creating during the casework. The policy for visitors and observation by outside experts is detailed in Appendix 2. This policy provided a framework when Dr. Henry Lee and Dr. Edward Blake came to the laboratory to observe removal of 10% of each sample which would be available for future testing. A single exception to our policy was ordered by Judge Ito which allowed Dr. Blake to personally remove the 10% of each sample which was to be saved. Later, Dr. John Gerdis also visited the laboratory to review information which was requested on discovery. Our discovery policy requires that all requests for discovery materials be communicated to us through our client (in this case the Los Angeles District Attorney's Office). Cellmark responds to each request indicating the existence, quantity and type of documentation and reproduction cost. This response is conveyed to the requesting attorney via our client. After payment arrangements are made, the items are sent to our client who can review the information and then forward the documents to the requesting attorney. For the case of People v. Simpson, approximately sixty pounds of documents were provided to the defense team in addition to copies of the case notes, records, photographs and autoradiograph copies. The known samples in this case were submitted as blood stains labeled C1, C2 and C3. DNA from these stains was extracted and quantities and quality of the DNA were evaluated by electrophoresis on a mini-gel. Using this routine technique, two of the stains showed evidence of degradation; DNA from the third stain was high molecular weight with no evidence of degradation. While this observation did not allow differentiation between the two victims, it was possible to deduce that the undegraded sample was more likely to be from Mr. Simpson than from the two victims. DNA banding patterns from each of the known individuals was analyzed on each of the three analytical gels alongside of the evidence samples and the results were reported in accordance with Cellmark's standard procedures. Of the original evidence samples submitted for RFLP testing, four were too degraded to be suitable for RFLP testing. One blood stain, the shoe print, appeared to contain high molecular weight DNA but did not produce an RFLP pattern. Another blood stain from the walkway at the Bundy crime scene showed a moderate level of degradation and RFLP analysis was attempted with this sample. A series of thirteen-day exposures using five highly polymorphic single-locus probes produced a DNA banding pattern which matched the DNA banding pattern obtained from the blood swatch C1 later identified as the known sample from Mr. Simpson. The blood stain taken from Mr. Goldman's boot produced an RFLP pattern which was consistent with being a mixture of DNA from Mr. Goldman and Ms. Brown. The DNA extracted by the California Department of Justice DNA Laboratory from the sock found in Mr. Simpson's residence was received at a later date and was also analyzed using five probes. This DNA banding pattern matched the DNA banding pattern from the known sample of Ms. Brown corroborating data already produced at the California Department of Justice DNA Laboratory. Fourteen evidence samples, three knowns and four substrate controls were analyzed at six loci using the polymerase chain reaction (PCR). The analysis was done using the AmpliTypeŽ PM PCR Amplification and Typing Kit and the AmpliType™ HLA DQA Forensic DNA Amplification and Typing Kit produced by Perkin Elmer. Following our Standard Operating Procedures, a reagent blank control was processed with each set of samples which used the same extraction procedure and were extracted simultaneously. Both positive and negative controls were amplified with each amplification performed. Additionally, four substrate controls were processed which had also been received as evidence. There are several important points which should be noted regarding the PCR-based analysis.
Although the PCR is an extremely sensitive technique, detection of multiple DNA sources in any given sample has definite limitations. Several factors affect the ability of the PCR-based tests to detect a second source. The use of genetic loci having higher levels of heterozygosity increases the probability that a mixture of two individuals will be detected. The ratio of DNA present from each source, the specific combination of genotypes and the amount of DNA amplified also effect the detectability of multiple DNA sources in a single sample. When using the DQA1 and 5 PM loci, mixtures are most easily demonstrated when three or more alleles are observed. However, sample mixtures can also be detected by differences in signal intensity at the 5 PM loci when only two alleles are observed. Validation studies done at Cellmark Diagnostics using DQA1, PM, and three short tandem repeat loci (STR) demonstrate that, in general, the minor component will not be detectable for mixture ratios below 1:20. Levels of detection for ratios below 1:20 are dependent on the genotypes which are combined in the mixture. Contaminants (i.e., an extraneous DNA source) must therefore be present at a certain threshold level before detection of that contaminant is a feasible explanation. The media attention to the court proceedings meant that many people would be listening to and commenting on the court testimony given by each witness. Additionally, the attorneys on both sides were knowledgeable about technical aspects of DNA identification procedures which meant that detailed technical answers articulated in plain language would be required. In preparation for testimony, some time was devoted to consideration of all the possible things that could go wrong. This was in addition to the usual pretrial preparation, including discussions with the attorneys, gathering of relevant scientific articles, and organization of the casework results and records. Despite the many distractions which were present, it became clear that the role of the expert witness in this trial was no different than it is in any other trial. The witness needed to listen carefully to the questions and provide clear, accurate and honest answers. Everything else was irrelevant. Wilmington, DE, July 25, 1994 - Cellmark Diagnostics, a business unit of Zeneca Inc., today confirmed its selection by Los Angeles law enforcement officials and the District Attorney's office to conduct the DNA analysis of evidence in the case of California v. O. J. Simpson. A company spokesperson said it is Cellmark's policy not to comment on cases currently in litigation. POLICIES FOR LABORATORY OBSERVATION BY OUTSIDE EXPERTS
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