Many products and technologies are specialized in the collection of evidence while others' sole purpose is to keep evidence organized. However, even fewer technologies can collect, organize, and provide the analysis tools all in one package. This is the main reason why 3D scanning for forensics is an ever growing and useful application of laser based measurement technologies in fighting crimes and reconstructing events. Like all forensic tools, however, 3D scanning has its strengths and its limitations.
Benefits of 3D Scanning in Forensics
It’s important to distinguish between data and evidence when capturing data with 3D scanners. 3D scanners are indiscriminate in their method of capturing data and can be viewed as "spray painting" the environment with thousands of dot measurements. However, not all data is evidence and unlike using a total station or taking hand measurements, a forensic technician can do a very detailed scan of an entire crime scene without the need to predetermine what areas of the scene contain true evidence. In some scenarios, evidence is quite obvious, but in others, "evidence" can be questionable or misleading. These often missed areas are captured in detail such that the resulting data set allows the crime scene to be reviewed at a later day by a forensic expert, who determines what is indeed evidence.
Aside from scanning speed, 3D scanners are particularly well suited for scanning organic shapes and highly curved surfaces that would otherwise be difficult to measure. In the case of bloodstains or "print" evidence that can span over several surfaces, furniture, and walls, trying to accurately measure evidence by hand can prove to be extremely tedious, inaccurate, and time consuming. Even with the use of a total station, the number of data points required would result in far too much time and effort when compared to the use of a 3D laser scanner.
A perfect example of this is in the analysis of bite marks located around the curved surface of an arm or other body part that is not perfectly flat. Photography is the traditional method of documenting bite marks, but there is no depth information contained in a photograph. Photography effectively takes 3D objects in the real world and projects them on a 2D image plane (i.e. the CCD on your digital camera) so that depth information is lost. The true nature of a bite mark can best be measured through the use of a close range scanner where the mark may wrap around the surface of an arm or hand. Thus, having the depth information and proper orientation of the bite mark on the surface of the body can provide the best possible "match" to a suspect.
Photography and casting are effective ways to capture footprints and other impression evidence. However, when the substrate is not a firm soil or hard material, the act of pouring a casting liquid into a print can effectively deteriorate the quality such that details are lost.