Forensic facial reconstruction

"Identity crisis"
Drewer, Brant, New Scientist, 27 February 1999

http://technology.newscientist.com/article.ns?id=mg16121754.500&print=true

Before investigators can even begin looking for suspects for a crime such as murder, it’s often important to be able to identify the victim. Sometimes all that is found are the skull and bones of the deceased. DNA analysis reveals nothing, dental analysis also fails to yield a missing person. In these circumstances, police resort to a technique known as forensics facial reconstruction to yield and photograph of what the deceased might have looked like.

Facial reconstruction as a technique to create 3-D facial approximations was first used by Welcker (1883). His (1895) was credited with advancing the technique as well as collecting data for the first table on average facial tissue thickness. This technique finds its origin in Biological anthropology and archaeology where it is still in use. Not till the mid 1960’s Wilton Krogman popularize the facial reconstruction in the field of forensics.

Two types of facial reconstuction exist today: two-dimensional and three-dimensional. 2D facial reconstructions are hand-drawn created from ante-mortem photographs and the skull. Tissue depth markers are place along the skull and photgraphs are taken. Drawing are done on a material known as Vellum. Computer programs F.A.C.E and C.A.R.E.S are now capable of creating 2D facial constructions much quicker .

3D facial reconstructions can be done in clay or under the computer. Construction with clay is a very slow and meticulous process, that begins with the creation of a plaster cast of the skull. Landmarks which correspond to particular spots on the unidentified skull are marked off on the cast. These sites represent the average facial tissue thickness for people of the same sex, race, and age as that of the remains. Next facial muscles are layered on the cast, followed by soft tissue of the neck, nose and then the lips. Muscles of facial expression and the soft tissue around the eyes, the ears are added next. Much fine tuning is done afterwards and finally a layer of flesh is added to mimic the skin. (To see a more complete and detailed procedure, search Taylor and Angel: Craniofacial Identification in Forensic Medicine, pgs 177-185)

Newer technology, described in the above article, “replaces knives with computers… and clay with a facial template.” This method is significantly faster than using clay and is more flexible(easier to modify.) First off, the skull is placed on a rotating table. A laser is projected on to the skull while it rotates. Ttwo cameras record the changing contours as the laser passes over the subject. Computers then triangulate the data collected by the cameras and creates a 3D image. Virtual pegs are place around the 3D image of the skull to delineate tissue depth. A facial template is then applied to the skull. At the Human Identification Centre of the University of Glasgow, the team of forensic pathologist choose from 200 templates: digitised faces of men and women, of different ages, build and race.

Finding the a suitable template is important because if the skull does not match the template. The template will become overstretched and this will cause distortions. To combat this problem, the team above aims to collect 3D Images of live people’s faces and their skulls from CT, MRI and ultrasound. With these images, researchers will try to calculate the distance between landmarks on the face and the skull. With this data technicians will be able to find a facial template for an unidentified skull based on calculated values rather than mere visual comparison. Through this same project they hope also to create a larger databases of facial templates.

Following matching a template, finer musculature is added and finally, the nose, the lips and the ears are added. These last three facial features are very difficult to recreate. Soft tissue degrades first thus no remants of these parts are usually found with the bones. Questions such as how long a person nose is? Did he/she smile much or were they generally angry of depressed are difficult and important questions to be tackled. Further study must be done. Creating a larger database of facial templates will hopefully reveal relationships between bone alignment/arrangement and the shape and size of the facial features that are more difficult to place.

Facial reconstruction continues to improve as technique that estimates what individuals may look like. More sophisticated computer algorithms will create more accurate reconstructions of individuals that otherwise have no other identification. Expert in the field generally agree that facial reconstruction will remain a tool for recognition and not identification. It will continue to provide a spark by creating a possible link between victim and family and friends but ulitmately other forensic techniques such as DNA analysis are needed to confirm identity.


For more information on:

3D -graphs see: http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6T6W-3YGDCHC-1-N&_cdi=5041&_user=489286&_orig=search&_coverDate=02%2F14%2F2000&_sk=998919997&view=c&wchp=dGLbVzz-zSkzk&md5=92f014e15ea6b5e1b8a7d7c951149129&ie=/sdarticle.pdf

Advance statistical modeling:

http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6T6W-4JGJJ88-5-R&_cdi=5041&_user=489286&_orig=search&_coverDate=05%2F15%2F2006&_sk=998409999.8998&view=c&wchp=dGLzVzz-zSkWz&md5=707a502a4c1f4d9efc8ece8952a58174&ie=/sdarticle.pdf