CCI Firearms and Toolmark Examiner Academy

1. CCI Firearms and Toolmark Examiner Academy Workshop on Current Firearms and ToolmarkResearch Pushing Out the Frontiers of Forensic Science

2. Outline • Morning-ish • Introduction and the Daubert Standard • Confocal Microscopy • Focus Variation Microscopy • Interferometric Microscopy • Surface Data/Filtering

3. Outline • Afternoon-ish • Similarity scores and Cross-correlation functions • Known Match/Known Non-Match Similarity Score histograms. False Positives/False Negatives/Error Rates • Multivariate Discrimination of Toolmarks • Measures of “Match Quality” • Confidence • Posterior Error Rate/Random Match Probability • Lessons learned in conducting a successful research project

4. Introduction • DNA profiling the most successful application of statistics in forensic science. • Responsible for current interest in “raising standards” of other branches in forensics…?? • No protocols for the application of statistics to comparison of tool marks. • Our goal: application of objective, numerical computational pattern comparison to tool marks Caution: Statistics is not a panacea!!!!

5. The Daubert Standard • Daubert (1993)- Judges are the “gatekeepers” of scientific evidence. • Must determine if the science is reliable • Has empirical testing been done? • Falsifiability • Has the science been subject to peer review? • Are there known error rates? • Is there general acceptance? • Federal Government and 26(-ish) States are “Daubert States”

6. Tool Mark Comparison Microscope

7. 4 mm G. Petillo G. Petillo

8. 5/8” Consecutively manufactured chisels Known Match Comparisons G. Petillo

9. 5/8” Consecutively manufactured chisels Known NON Match Comparisons G. Petillo

10. 5/8” Consecutively manufactured chisels 4 mm 4 mm 600 um

11. Confocal Microscope Marvin Minsky First confocal microscope

12. Confocal Microscopes

14. Source In focus light Illumination aperture Out of focus light Detector Confocal pinhole Objective lens Tool mark surface (profile of a striation pattern) Focal plane for objective Sample stage

15. Rastering pattern of laser confocal Nipkow disk sweeps many pinholes

16. Programmable array Illumination/Detection Get any illumination/detection pattern

17. Objective’s focal plane Scan stage in “z”-direction Sample stage

18. Detector Objective’s focal plane Scan stage in “z”-direction Sample stage

19. Detector Objective’s focal plane Scan stage in “z”-direction Sample stage

20. Detector Objective’s focal plane Scan stage in “z”-direction Sample stage

21. Detector Objective’s focal plane Scan stage in “z”-direction Sample stage

22. Detector Objective’s focal plane Scan stage in “z”-direction Sample stage

23. Detector Objective’s focal plane Scan stage in “z”-direction Sample stage

24. Detector Objective’s focal plane Scan stage in “z”-direction Sample stage

25. Detector Objective’s focal plane Scan stage in “z”-direction Sample stage

26. Detector Objective’s focal plane Scan stage in “z”-direction Sample stage

27. Detector Objective’s focal plane Scan stage in “z”-direction Sample stage

28. Detector Objective’s focal plane Scan stage in “z”-direction Sample stage

29. Detector Objective’s focal plane Scan stage in “z”-direction Sample stage

30. Detector Objective’s focal plane Scan stage in “z”-direction Sample stage

31. Detector Objective’s focal plane Scan stage in “z”-direction Sample stage

32. Detector Objective’s focal plane Scan stage in “z”-direction Sample stage

33. Detector Objective’s focal plane Scan stage in “z”-direction Sample stage

34. Detector Objective’s focal plane Scan stage in “z”-direction Sample stage

35. Detector Objective’s focal plane Scan stage in “z”-direction Sample stage

36. Detector Objective’s focal plane Scan stage in “z”-direction Sample stage

37. Detector Objective’s focal plane Scan stage in “z”-direction Sample stage

38. Detector Objective’s focal plane Scan stage in “z”-direction Sample stage

39. Detector Objective’s focal plane Scan stage in “z”-direction Sample stage

40. For Each Detector Pixel: Detector Point on surface corresponding to pixel’s is in maximum focus here Record the “axial response” as stage is moved along the z-direction

41. Increasing surface height All-in-Focus 2D Image Overlay confocal “z-stack”

42. 3D confocal image of portion of chisel striation pattern

43. Confocal Microscope Trivia • Use high NA objectives for best results • Small working distances • Flanks up to ~ 70o • Cost ~150K – 250K (FTI IBIS ~1M) • Get a vibration isolation table for your instrument ~7K • Set up in a (dry) basement if possible • Accuracy down to +/- 10 nm Optical slice thickness =

44. Confocal Microscope Trivia • Some manufactures: • Olympus • LEXT (Laser) • Zeiss • CSM (White Light) • LSM (Laser) • Nanofocus • msurf series (White Light) • Sensofar/Leica • Plu series/DCM (White Light)

45. Focus Variation Microscope “Low res” common Focus variation mic ~ +/- 1mm Scherer and Prantl

46. Detector In focus light Source Out of focus light Objective lens Tool mark surface (profile of a striation pattern) Focal plane for objective Sample stage

47. Cutaway Alicona, GMBH

48. Objective’s focal plane Scan stage in “z”-direction Sample stage

49. For Each Detector Pixel: Detector Point on surface corresponding to pixel is in maximum focus here Record the “axial response” as stage is moved along the z-direction

50. Focus Determination: Detector Pixel of interest Compute standard deviation (sd) of pixels grey values in the neighborhood A pixel in focus sits in a neighborhood with a large sd