Trial Preparation:

review of all case documents and data

Discovery Requests of Vital Case Documents: Maximizing the effectiveness of case review by SFR will require a discovery request for more than just one or two brief crime lab reports. Labs often require a court order as a prerequisite to the release of copies of various key analytical documents. Through utilization of the discovery process, SFR will assist you with initiating and executing a thorough examination of your case. Copies of the following case documentation, where applicable, should be requested via discovery:

• Evidence Screening/Examination (Serology) Report
• DNA Profile Analysis Report
• Evidence Item Lists - Examined Items & Unexamined Items
• Laboratory Case Notes/Analyst Bench Notes
  (often handwritten)
• Evidence Screening/Examination (Serology) Worksheets
• DNA Worksheets-Extraction, Quantification, PCR Analysis, etc.
• STR Typing Data - Electropherograms, Gel Scans, etc.
• Genetic Loci STR Allele Call Summaries
• DNA Mixture Analysis (See SFR Policy-summarized below)
• Population Statistical Calculations
• Positive and Negative Controls
• Laboratory Standard Operating Procedures-Particularly their RFU limits for Capillary Electrophoresis
• Chain of Custody For Pertinent Case Items
• Pertinent Reports From Law Enforcement or Medical Facilities
• Communications - Analysts, Supervisors, Investigators, Prosecutors, etc.

SFR POLICY ON DNA MIXTURE INTERPRETATIONS

Among the cases involving disparities associated with DNA analysis, the presence of complex DNA mixtures on key evidence items is often at the center of the controversy. For this reason, Spence Forensic Resources has outlined a policy on scrutinizing and interpreting DNA mixtures observed by the reporting laboratory. The steps for these interpretations are as follows:

Step 1: Analysis of electropherogram data to ensure that the profile in question is, indeed, a mixture. When a single source DNA profile from an evidence item matches the profile of a known reference standard, with the exception of ONE additional allele, it is my opinion that no statistical conclusions should be drawn from that single allele. This is especially true when the single allelic peak height is relatively low, or can potentially be attributed to an artifact of the PCR process or capillary electrophoresis.

Step 2: In the event that a genuine mixture is being called, SFR will evaluate the mixture for the possible presence of a major profile, plus one or more minor profiles. The alternative to this would be the apparent presence of NO major profile, ONLY minor, indistinguishable sources of DNA. This evaluation is dependent upon a detailed assessment of the peak height landscape of the entire mixture profile electropherogram-with consideration of the potential contributing reference standard profiles. A final determination will be at the discretion of the analyst, based on years of experience in evaluating hundreds of DNA profiles.

Step 3: If three alleles are present at two or more loci, the mixture includes at least two individuals. If five alleles are present at one locus or more loci, the mixture includes at least three individuals. If seven alleles are present at one locus or more loci, the mixture includes at least four individuals, and so on.

Step 4: On a case by case basis, SFR will evaluate of the capacity of each mixture to be interpreted through sound, reasonable, scientific methods. A variety of factors can contribute to the conclusion that a DNA mixture is simply unsuitable for a reliable interpretation. These factors include, but are not limited to the following: 1) The number of contributors to the mixture-the greater the number of total alleles observed, the less potential there is for a reliable statistical conclusion. 2) When indistinguishable minor contributors are relatively equal donors of DNA, little can be gained from scrutinizing allelic imbalances. 3) When alleles overlap, such as might be expected from contributors who are genetically related or from the same ethnic population pool. 4) When one or more unknown individuals have contributed to the mixture profile, i.e. they have donated DNA alleles that cannot be correlated with the available known reference standards. 5) Allelic dropout has to be assumed in order to make non-exclusion calls.

Step 5: In the event that a genuine mixture is called, the degree of allelic dropout may be cautiously evaluated for the potential exclusion of each suspected contributor. When a key suspect or victim reference standard profile is to be compared to a DNA mixture, the absence of ONE allele from the mixture could be evidence for potential exclusion. An example of this would be that Suspect A has a 9, 11 DNA profile at a given locus. In the mixture profile, a 9 allele-with a substantial peak height-is observed that cannot be attributed to any other suspected contributors to the mixture. Meanwhile, there is a clear absence of an 11 allele in the mixture. Observation of additional dropout events corresponding to Suspect A would further strengthen the cause for exclusion. By assessing the peak height landscape of the DNA mixture electropherogram and the number of apparent allelic dropout events, SFR will utilize years of experience-evaluating hundreds of DNA mixture profiles to arrive at decisions on exclusion or non-exclusion.

Step 6: When a mixture is judged to be suitable for interpretation and there is insufficient evidence for exclusion, the probability of exclusion will be calculated for the mixture. If there is evidence of allelic dropout at a particular locus, that locus will not be used in the probability of exclusion calculation for the mixture.

CONSULTATIONS, CASE REVIEWS, REPORTS

AND TRIAL PREPARATION

Once all of the pertinent case documentation has been obtained and carefully reviewed, and all DNA mixtures have been interpreted, SFR might recognize the need for additional documentation from the crime lab. Areas requiring further review might include any of the following: Lab quality assurance documents and technical manuals; additional review of standard operating procedures (SOPs); validation studies; lab diagrams demonstrating separation of work areas; qualifications for personnel conducting the case supervision, analysis, or review; proficiency test results; copies of computer data files; genetic databases and allelic frequency tables used for statistical analysis; lab records for equipment maintenance, troubleshooting, reported errors, and corrective actions; lab accreditation and audit documents demonstrating compliance or non-compliance with standards for forensic DNA testing laboratories.

Once the review process is complete, SFR will generate a report. This report will summarize the strengths and weaknesses of the data recovered from the case evidence. The report will also identify any issues associated with the reliability of the analysis, the accuracy of the data, or the significance of the conclusions. In some instances, it might be useful for SFR to summarize complex DNA data and the significance of analytical conclusions in the form of a PowerPoint presentation. Informal discussions, official reports, and visual presentations prepared by SFR, all serve as effective tools in the event that courtroom testimony becomes necessary.