Forensic Sci Med Pathol (2011) 7:53–62 Fig. 20 Cut-off saw blade kerf Fig. 21 Boxplot of kerf widths. 1. Portable band saw, 2. Hack saw, 3. Bow saw, 4. Molding cut-off saw, 5. Meat saw, 6. Jig saw, 7. Reciprocating saw, 8. Hand saw, 9. Circular saw, 10. Cut-off saw. (For boxplot values, the top line represents the maximum width, next down the 3rd quartile, median, 1st quartile and lastly the minimum width. Also some boxplots have an outlier which is indicated by ‘‘O’’) Also, the molding cut-off saw kerf width had only a 10% chance of originating from the molding cut-off saw and an 83% chance of originating from the bow saw. In summary, statistical Model #2 is a more accurate model for predicting Table 1 Blade and teeth width (mm) characteristics for non-powered and electrical saws Saw types Hand saw Hack saw Meat saw Bow saw M. cut-off Reciprocating Skill saw Cut-off saw P. band saw Jig saw Blades 0.940 0.610 0.635 0.889 0.635 1.016 1.397 1.905 0.635 0.940 Teeth 1.400 0.660 0.914 0.914 0.889 1.397 2.083 2.667 0.660 1.143 59 Differences 0.460 0.050 0.279 0.025 0.254 0.381 0.686 0.762 0.025 0.203 the possible saw types based on kerf widths used in this study. The logit models have limitations when some kerf marks cannot be separated. Therefore, the logistic regression provides an estimated probability of each category and it is possible that two or more categories may share similar probabilities given a speciﬁc covariate value, namely, the kerf width. When the categories are not separable, there may be a higher false probability rate. For example, in Model #1 the bow saw and molding cut-off saw present limitations due to similarities of the kerf marks. Also, in Model #2 the kerf marks produced by the bow saw and molding cut-off saw present limitations because they can- not be separated. However, the logit models provide like- lihoods for each saw type given the limitations. Discussion Saw characteristics affecting the kerf width and bone sur- face adjacent to the kerf include style and design of the teeth, width of the teeth, teeth per inch (tpi), degree of wear on the teeth, saw cutting speed, blade vibration, defects in the blade or erratic sawing motion. Also, a worn bushing in mechanical-powered saws can affect kerf widths. With the exception of band saw type saws, mechanical-powered saws generally require thicker blades than human-powered saws due to saw power and operating speeds. Conse- quently, these saws produce broader kerf widths than human-powered saws [13–15]. Additionally, ﬁre can alter tool marks on bone. For example, ﬁre can result in a loss of structural integrity causing bone to easily fracture. It can obscure some of the individual and class characteristics and also cause shrink- age in bone [16–18]. Bone shrinkage will affect saw blade predictions based on kerf widths. 123