For JANUARY 2000 issue

SCIENCE IN CRIME DETECTION

Taking post-mortem X-rays of the skull

‑Dr. Anil Aggrawal

The new millennium is arriving, and everyone is waiting anxiously, and with new hope for the new millennium. The first article of the new millennium is the 80th (an interestingly round figure!) in our series “Science in Crime Detection”. As this is the first article of the new millennium, I want to make it somewhat special. And that is why I am giving a special forensic technique in this issue.

Many times, we have to take a postmortem x-ray of the skull. You might be surprised why such a strange procedure is required at all. In a country, where it is difficult to get X-rays done even for living persons, what purpose is served by taking X-rays of a dead person. Well, there are many purposes and this is the basis of this month’s article.

Imagine that five people are missing from a particular village or a locality. Three of them are girls and two boys. It is quite possible that these five people have run away from their families over some disputes. But it is equally likely that they have been murdered by some person and the dead body has been disposed off. Now imagine that a villager on one fine day finds a skull in some bushes. Now the natural suspicion of all villagers would be that this skull could belong to either of these five missing people. Doctors can examine the skull closely and can say whether the skull belongs to a male or a female. So as far as the question of sex is concerned, the doctor can help the police. But remember that three girls and two boys are missing. So it the doctor, say, tells the police that the skull belongs to a boy, that still leaves two boys, and the police would want to know which of the two boys the skull belongs to.

The doctor can not say this merely by naked examination of the skull. It is here that post-mortem radiography – the topic of this month’s article – comes in handy. Before proceeding further, I would like to tell you that certain air spaces in the skull, situated behind the forehead are quite unique in each individuals. Technically these air spaces are known as frontal sinuses. These sinuses look rather like a bunch of inflated balloons of different shapes and sizes. Normally the function of these sinuses is to keep the skull light, and to make it more resonant. It is partly because of these sinuses, that our face shapes are different. These sinuses are unique in all individuals. Thus if an X-ray of your and my skull are taken, the frontal sinuses would be different in both the skulls. In fact, it has been alleged that the frontal sinuses of all individuals in this world are different. These frontal sinuses are very clearly visible in X-rays, but if you have to actually see them in the skull, you would have to break the skull to see them.

Another thing I would like to tell the gentle reader, before I proceed further. Even the shapes and sizes of teeth in all the individuals are different. Other things such as diseases of the teeth, carious teeth, root canal treatments, etc all make the teeth further highly individualistic. Although all these things – such as root canal treatments – are difficult to see by naked eye examination, these changes appear very well in the X-rays.

In modern world, most people go to doctors for minor ailments, and doctors advise them X-rays. It is quite possible that these boys had also gone to the doctor sometime in their life for some treatment, and the doctor had advised X-rays to them. If such X-rays of the skull are available with the family, it becomes very easy for the doctor to identify the skull.

The idea is to take an X-ray of the skull (which was found in the bushes), and to compare this X-ray to that available with the two families. Taking X-rays of the skull is not a simple matter and requires some specialized techniques.

First of all, the skull is fixed in a special machine called cephalostat. Look at figure 1, where the skull is found attached to cephalostat. The lower jaw is loose in a skull, and to keep it attached to the rest of the skull, the forensic specialist may apply some pads of silicone rubber. Upper and lower teeth can also be held together using Plasticine. Note in figure one that the X-ray film is on the right side.

Figure 2 shows an X-ray of this skull which was taken. Figure 3 shows the position of skull for taking X-rays in a slightly different position, and figure 4 shows the X-ray taken in that position. Now these X-rays can easily be compared with the X-rays taken during the life of the person. If the frontal sinuses of the skull match with, say the first boy, the specialist can positively say that the skull belongs to him, and the police can start investigation in that direction. If the X-rays of the skulls do not match, the skull would obviously belong to the second boy. In the rare instance when the X-ray of the skull does not match with that of either of the boy, the police would have to look for some other possible victim. This procedure makes it very easy for the doctor to identify the victim, even from his skull.

The doctor can double check by taking the X-rays of the teeth also. Figure 5 shows how the lower jaw (called mandible in the medical parlance) can be placed and an X-ray taken. In this figure, the mandible is kept upside down ( note the teeth touching the table). The X-ray tube can be seen on the upper left hand side. Figure 6 shows the X-ray of the lower teeth taken in this fashion. If the teeth show some special disease, which was present in one of the victims, the identity can be positively established.

Figure 7 and 8 show two more specialized ways of taking postmortem X-rays of the teeth of the individual. These give different views of the teeth, and make things somewhat easier for the forensic specialist.

Last year a case was brought to me, in which the police found two skulls lying on a riverside. Some days back a lover couple had disappeared from the nearby areas, and there was a strong suspicion that these skulls belonged to that couple. However, about 14 more people had reported drowned in that river at different periods, and it was quite possible that the skulls could belong to any of those fourteen people too. The relatives of the couple refused to believe that these were the skulls of their relatives. There were questions of inheritance involved too. Thus the whole scene became very much charged with emotion. The police approached me with the skulls and asked me if I could tell whether the skulls belonged to that couple or not. I applied the same procedure in that case, and could positively say that the skulls belonged to that couple. My conclusions were based on certain special characteristics of the teeth of the two individuals which were recorded in the X-rays taken during their life. The police accepted my findings and started finding the killers of the couple. Very soon three goons were arrested, who had accosted the couple some days back in the night. They were basically small time crooks looking for some valuables and money. But when they saw a beautiful girl, they could not contain themselves. They first killed the man; then raped the girl turn by turn, and when they had done the misdeed several times, they killed her too. Thus it was my analysis of the skulls of the two individuals which could establish their identity and it was on that basis that the killers were caught.

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Captions of figures

001: Skull in a cephalostat. The mandible has small pads of silicone rubber replacing the lost cartilaginous discs of the temporomandibular joints. The anterior teeth are temporarily held in their sockets using Plasticine. The film cassette is on the right of the field.

002: Typical post-mortem lateral cephalometric view of a skull disarticulated from the axial skeleton. The absence of soft tissue negates the need for an aluminum step wedge over the face, and considerable adjustments need to be made to typical exposure settings. Two radiographs may still be required to image all parts of the specimen adequately.

003. Skull in a cepahlostat aligned for an antero-posterior view. The skull can be rotated 180 degrees to facilitate posteroanterior views, which are more likely to correspond with available ante-mortem records.

004. Radiograph of the skull. The radio-opacity of dental restorations obscures some detail in this projection. Similarly, the aligning rod placed at the root of the nose masks the frontal sinus outline. If this is removed, care needs to be taken to stabilize the skull and prevent rotation about the ear rods.

005. Mandible disarticulated from the skull making it easier to take anterior occlusal views of the mandibular dentition. Note the use of boxes covered with a towel to achieve the necessary orientation of the jaw.

006. An example of the radiograph obtained using the configuration and positioning of the specimen in figure 005. Radiographs of the skeleton divested of all soft tissue show excellent contrast and fine bone and dental details.

007. A human skull showing the position of an intra-oral film holder. This demonstrates the use of Plasticine to hold the teeth within their sockets and rubber bands to mimic the muscles of mastication.

008. Same skull as that shown in figure 007, demonstrating the position and use of a cone-centering device. This ensures the production of consistent, reproducible radiographic projections during test exposure.

(Dr. Anil Aggrawal, M.D. is a Professor of Forensic Medicine at the Maulana Azad Medical College, New Delhi. His E-mail is dr_anil@hotmail.com, and his website is http://members.tripod.com/~Prof_Anil_Aggrawal/index.html)