Insights to enhance the examination of tool marks in human cartilage

Abstract

This work deals with the examination of tool marks in human cartilage. We compared the effectiveness of several cleaning methods on cut marks in porcine cartilage. The method cleaning by multiple casts achieved the significantly highest scores (P = 0.02). Furthermore, we examined the grain-like elevations (dots) located on casts of cut cartilage. The results of this study suggest that the casting material forms these dots when penetrating cartilage cavities, which are areas where the strong collagen fibres leave space for the chondrocytes. We performed fixation experiments to avoid this, without success. In addition, 31 casting materials were compared regarding contrast under light-microscope and 3D tool marks scanner. Under the light-microscope, brown materials achieved significantly higher values than grey (P = 0.02) or black (P = 0.00) whereas under the 3D scanner, black materials reached higher contrast values than grey (P = 0.04) or brown (P = 0.047). To compare the accuracy and reproducibility of 6 test materials for cartilage, we used 10 knives to create cut marks that were subsequently scanned. During the alignment of the individual signals of each mark, the cross-correlation coefficients (Xmax) and lags (LXmax) were calculated. The signals of the marks in agarose were aligned with significantly fewer lags and achieved significantly higher cross-correlation coefficients compared to all tested materials (both P = 0.00). Moreover, we determined the cross-correlation coefficients (XC) for known-matches (KM) per material. Agarose achieved significantly higher values than AccuTrans®, Clear Ballistics™, and gelatine (all P = 0.00). The results of this work provide valuable insights for the forensic investigation of marks in human costal cartilage.

Quantitative matching of forensic evidence fragments utilizing 3D microscopy analysis of fracture surface replicas

“…A Mikrosil gray silicone type casting material was utilized in generating the fracture surface replicas because it is one of the common replication materials for forensic analysis [19,42,45]. The Tip surface was replicated for the entire set.…”

“…During the last two decades, new innovative 3D surface topological scanning microscopy has been developed with the potential to improve physical matching. Different 3D acquisition systems, employing 3D laser scanners, optical coherence tomography, stylus scanning instruments, and confocal microscopy, have been utilized for forensic evidence identification applications [19,26,29‐43]. Automated surface acquisition and matching processes utilizing 3D topography data have demonstrated promising improvements in the objectivity of the comparison process [34].…”

“…Zooming out from the profile (looking at longer wavelengths, or spacing between topological events) makes the profile appear smoother, while zooming in on the profile (looking at shorter wavelengths, or spacing between events) results in the 2D profile appear rougher and makes it possible to identify unique features for forensic comparison. Further, forensic replicas utilizing silicone casts are widely used by practitioners in the comparative analysis of physical forensic articles [18,42,44,45] and for tool marks on human tissues [19][20][21][22][23][24]. However, there is a dearth of in-depth analysis of the ability of a silicon cast to reproduce a useful range of topographical details needed for 3D analysis [19].…”

“…Further, forensic replicas utilizing silicone casts are widely used by practitioners in the comparative analysis of physical forensic articles [18,42,44,45] and for tool marks on human tissues [19][20][21][22][23][24]. However, there is a dearth of in-depth analysis of the ability of a silicon cast to reproduce a useful range of topographical details needed for 3D analysis [19]. Especially, the silicon cast of a fracture surface may not replicate all the small features that represent the short-wavelength topology of the original surface.…”

“…In particular, we identify the ranges of wavelength and frequencies that it replicates to perform quantitative forensic fracture matches. In optical microscopy, it will set the proper magnification to view the replicated surface and the number of replication materials for forensic analysis [19,42,45]. The Tip surface was replicated for the entire set.…”