Helical Forensics LLC
Forensic Biology / DNA Expert Consulting
TRIAL CONSULTATION SERVICES
Criminal Case Evaluation:
Review and examination of case file information including police reports, witness statements, crime scene photographs, evidence collection and handling procedures, chain of custody documents, forensic laboratory reports, autopsy reports, etc.
DNA Laboratory Case Review:
Two primary questions that need to be answered when reviewing and examining the DNA laboratory records for a specific case are: Does the data support the conclusions in the final laboratory report and how do these conclusions help explain what happened in the incident? Therefore, it is necessary to review and examine the DNA laboratory standard operating protocols, the laboratory analyst’s handwritten evidence examination notes, evidence sketches and photographs, serology testing worksheets, DNA testing data upon which the final conclusions are based, the source of the population frequencies and evidence of their validity, equipment maintenance records, corrective action records, precautionary measures, final laboratory reports, communication logs, chain of custody documents, documentation regarding evidence handling, sampling, and storage, etc. Depending on the results of the review, independent testing of remaining evidence samples may or may not be recommended. Unless the DNA analysis is severely flawed, independent testing would unlikely produce different results. However, independent DNA testing might be required in the following instances: a) incorrect interpretation of the DNA data or an inappropriate analysis performed by the laboratory, b) probative evidence items that were never tested, c) when the only evidence is a match with a DNA profile in the CODIS database, and d) additional genetic markers might indicate differences between the evidence and reference samples.
DNA stands for Deoxyribonucleic Acid and is the genetic material that stores the inherited traits that are passed on from one generation to the next. The primary type of DNA found in the cells of the body that is tested in forensic laboratories is nuclear DNA. Nuclear DNA is a linear molecule that is packaged in chromosomes within the nucleus of the cell. Humans have 23 pairs of chromosomes – half of the chromosomes are inherited from the mother and half are inherited from the father. Current forensic DNA testing combines PCR (Polymerase Chain Reaction) with STR (Short Tandem Repeat) analysis of those locations in human DNA that differ between people. Approximately 99% of all human DNA is the same. The one percent of DNA that differs between each person contains sequences of repeating nucleotides called Short Tandem Repeats (STRs). STR regions (or markers) are short sequence elements that repeat themselves within the DNA molecule. What is important to forensic biologists is that STR regions are highly polymorphic, which means they are different between people. These repeat sequences are relatively short in length, typically 2-6 bases and the entire STR region is very short (less than 500 bases in length), which means that STRs are less susceptible to degradation and may often be recovered from trace amounts of biological material. Although there are thousands of STR markers that have been identified through genomic research, the FBI has established a standard set of STR locations (or loci) for forensic DNA testing and statistical calculation purposes and are required by the FBI’s National DNA Index System (NDIS). These locations along the DNA molecule are composed of STRs found on different chromosomes and the number of times each STR is repeated at all of the loci constitutes a DNA profile. This type of forensic DNA testing is the most commonly used method and involves a four-step process – extraction, quantitation, amplification, and detection. Once the analysis is complete, the DNA profile that is generated from a piece of biological evidence can be directly compared to the DNA profile from a reference sample from a victim or suspect to determine whether the person is included or excluded as the source of the biological material. DNA profiles generated from evidentiary items can also be uploaded to the CODIS database and searched against other unknown DNA profiles from other cases as well as compared to DNA profiles of convicted offenders. This is a powerful investigative tool, especially in non-suspect cases. Other types of DNA testing utilized in criminal cases include Y-STR and mitochondrial DNA analysis.
Y-STR analysis is specific to the Y chromosome and detects only male DNA – an invaluable investigative tool when a mixture of female and male DNA is present and the female is the major contributor (e.g., sexual assault cases). However, since the Y chromosome is paternally inherited, every male individual in the same paternal lineage will be expected to share the same Y-STR profile. Because of this, the resulting statistics are not as discriminatory as those typically found in autosomal DNA testing. Y-STR analysis is also used in genealogical DNA testing.
Mitochondria are cellular structures found in all of our cells. They are known as the “power plants” of our body, providing approx. 90% of the energy that body needs to function. Each cell in our body contains hundreds to thousands of mitochondria, each containing several loops of DNA. Therefore, since each cell in our body can have thousands of copies of mitochondrial DNA (mtDNA), mtDNA analysis has become a powerful tool in forensics for identifying human skeletal remains (including bones and teeth) as well as hairs without roots. mtDNA is present in high copy number within cells, is located outside the nucleus, and is maternally inherited. Because mtDNA is maternally inherited, every individual in the same maternal lineage will be expected to share the same mtDNA profile, with a few exceptions (i.e., heteroplasmy). mtDNA analysis is utilized when the quality and/or quantity of DNA from biological evidence samples is insufficient for nuclear DNA testing, which may occur in old, degraded, and environmentally damaged samples. mtDNA analysis can also be used in cases where maternal relatives are the only available source for reference samples (e.g., cases involving missing persons or mass disasters). The results of mtDNA analysis can provide an important link between victim, suspect, and/or crime scene and can conclusively exclude an individual as the source of a mtDNA profile. The majority of mtDNA analysis involves hair evidence where only the hair shaft is present. Because mtDNA analysis is a destructive process that can consume evidence samples, identifying information from hairs and skeletal remains needs to be documented prior to testing.
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Laboratory Assessment and Evaluation:
On-site witnessing and observation of laboratory testing of limited evidence samples which includes ensuring adherence to proper protocols regarding evidence handling, serology testing, DNA analysis, etc.
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Pre-Trial Consultation:
Assist legal counsel in developing their case theory and trial strategy through evaluation and assessment of expected testimony, moot court exercises, and developing cross-examination questions for crime scene personnel, forensic experts, and other key witnesses. Pre-trial consultation services also include review of court transcripts, evaluation and assessment of the scene investigation, examination of forensic laboratory testing records, interpretation of scientific findings, relating the physical evidence to the reported actions and events in the case, providing recommendations for additional forensic testing, helping to develop cross-examination questions for fact witnesses and opposing experts, helping to develop voir dire questions for potential jurors, and participating in pre-trial interviews of witnesses.
Trial Consultation:
Listen to the testimony of fact witnesses and opposing experts and advise legal counsel on cross-examination and provide ideas for closing argument.
Expert Witness Testimony:
Direct expert testimony in the areas of biological evidence collection, forensic serology, forensic DNA analysis.
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Educational Training:
Instructional seminars on the basic principles, theory, and application of biological evidence collection, forensic serology testing, and forensic DNA analysis.