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News from the front: Adventures in Forensic Science

News from the front: Adventures in Forensic Science. Keith Inman Forensic Analytical Specialties, Inc. We must understand what this is about, or we will make mistakes!. source evidence target. Source-Evidence-Target. target. evidence. source. Issues.

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News from the front: Adventures in Forensic Science

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  1. News from the front:Adventures in Forensic Science Keith Inman Forensic Analytical Specialties, Inc.

  2. We must understand what this is about, or we will make mistakes!

  3. source evidence target Source-Evidence-Target target evidence source

  4. Issues Too much reliance on experience, too little on experimentation Failure to pose hypotheses/proper questions Poor documentation Failure to understand limits Failure to understand the null hypothesis Failure to know where you are in the forensic paradigm Failing to understand inference and deduction Failure to understand the law and the science

  5. Bias • Who asks the question • What assumptions are made • What is a blind read, and who makes it • Failure to know what part of the paradigm your operating in

  6. Which came first, the blood or the print?

  7. “Was the stain drops or smears?”

  8. Is there doggie DNA on swab?

  9. Is the father’s semen on the daughter’s panties?

  10. Current Practice Request: Please test the bloodstain for DNA and compare to Keith’s reference sample

  11. Current Practice • Applied Science response: Photo, extract, run 13 CODIS STR loci. Issue report indicating match, with RMP of 10-17

  12. Current Practice Scientific Method response: Test with special blend of PCR primers for X-specific markers using 40 cycles. Find low-level mixture of 1 male and 1 female. Writes report disputing public lab results.

  13. Paradigm Request: Please test bloodstain for DNA and compare to Keith’s reference

  14. Paradigm • Read police reports/call detective • Carl’s shirt • Carl hit Keith in mouth, gets Keith’s blood on Carl’s shirt • Carl told detective the blood is from a nosebleed he (Carl) had yesterday • Carl’s wife confirms nosebleed • Keith and Carl are identical twins

  15. Paradigm • Pose reasonable competing hypotheses • Keith’s blood is on the shirt from blow to the mouth from the fight • Carl’s blood is on the shirt from the nosebleed the day before • Neither Keith nor Carl’s blood is on the shirt

  16. Paradigm • Articulate assumptions: • Shirt collected and preserved properly from Carl after the assault • Proper safeguards practiced by law enforcement to prevent contamination • It’s Carl’s shirt • Keith and Carl are identical twins • No strong competing DNA on substrate

  17. Assumptions (cont) • The blow to Keith created a bleeding wound in a location that would spatter or transfer • Carl was wearing the shirt in a normal fashion.

  18. Paradigm • Examine stain for BSP • Stain on outside, supports either hypothesis • Determine if Keith is bleeding, and from where • Keith has split lip • Confirm twin-ness of Keith and Carl • They are

  19. Paradigm • Look for nasal secretions in stain • No such test exists • Consult with University researcher to develop and validate one

  20. Paradigm • Evaluate hypotheses in light of test results • Evidence supports both hypotheses equally • Further test are required to differentiate between hypotheses • Any change in assumptions, or more facts, could change the interpretation and suggest definitive tests

  21. Summary • Viewing DNA typing in a case context can help define and clarify the questions • The Forensic Paradigm can help structure the inquiry in the context of the case

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