4. Conclusions
We have presented a novel method to fabricate planar replicas of the lateral surface of a shot bullet.
The advantage of the produced samples is that they display in a straight plane the negative topography of the whole striae landscape preserving their three dimensional nature and just removing the large scale curvature or deformation that is due to the bullet shape (in
particular when they have been subjected to strong impacts).
This method proves to be valuable because it allows one to produce an arbitrarily large number of copies of the original ballistic evidence that can be thus preserved from damaging due to manipulation.
All these copies can be exchanged between the different law enforcement agencies for their own analysis.
We have shown how these samples allow to overcome some of the drawbacks arising when dealing with original bullets collected on the crime scene; in particular their surface together with their flat shape avoid the artifacts that could be provided by the combination of a far from optimum illumination on a reflective metallic non planar surface and by a non precise sample mounting on the manipulator that can distort the microscopy images.
The comparison in a single image of the whole striae sequence displayed by the bullet lateral side allows a very fast first order comparison in terms of their class characteristics (land and groove impressions) that can then be pushed to the individual characteristics (striae) impressed by rifled barrels by simply going to higher magnification images.
The PSDF of these images has also been compared to show how the position of their main characteristic lengths can be associated.