For February 1999 issue

SCIENCE IN CRIME DETECTION

HOW IS EXPLOSIVE SABOTAGE DETECTED?

-Dr. Anil Aggrawal

I have just returned from a Forensic Medicine conference in Bijapur where I met a number of forensic experts. I was very pleased and satisfied to know that most of them were following my monthly column in Crime & Detective. They all liked the column very much. I asked what more they specifically wanted in my columns and I was told that I should regularly update them on the latest additions in forensic literature.

This time I am recommending the readers a very good book on explosive investigation that has recently come in the market. It is “Forensic Investigation of Explosions” edited by Alexander Beveridge (Editor: Please reproduce figure 1.jpg here). This book explores all aspects of explosive investigations, but I am going to concentrate on explosions occurring within aircrafts. This book describes this kind of investigation very nicely.

Most modern jetliners cruise at high altitudes – almost 6 miles high. The speed is also very high. It is almost 85% of the speed of sound, or almost 575 miles per hour. At such high speeds, any type of explosion can scatter the aircraft rubble over a vast area. An average aircraft has about 200 tons of structure, 100 tons of fuel and about 50 tons of cargo and passengers. If an explosion occurs on board, all this stuff can be scattered over a very wide area and the very first step in any subsequent investigation would be to recover the remains of the aircraft. Almost all clues relating to the cause of explosion would be found in these remains only.

Explosions may occur accidentally also, but they may be engineered with criminal intent too. In the latter case, it becomes imperative to find out the cause of explosions- especially who (or which organization) was responsible for the explosion. A proper investigation can lead to catching the criminals, thereby ensuring that such instances are not repeated.

Between 1961 and 1994, there were approximately 1553 fatal airline accidents which resulted in 41,730 deaths. During the same time, there were approximately 58 cases and 1812 deaths where aircraft were damaged or destroyed by the detonation of an explosive device within the aircraft. These statistics remind us that the problem of explosions occurring in an aircraft (with criminal intent or otherwise) are not to be taken lightly, and a proper investigation is a must.

One of the biggest explosions in flight occurring in recent years was that occurring on 21 December 1988. The aircraft which crashed was being operated as a commercial civil airliner on a flight designated as PA103 from London Heathrow to New York (Editor please reproduce figure 2.jpg here). This was a typical case of explosion occurring on board, where all kinds of investigative devices were used. A sterling work was done. It is estimated that at least 17 million pound sterlings were spent on investigations. This gives us an indication how thorough the investigation of such cases has to be. In our own country we must strive for similar standards.

Most of the investigation deals with the recovery of the rubble. If the rubble – including human bodies – can be recovered successfully, chances are that the cause of explosion can be found accurately.

One of the techniques utilized is SONAR. It is an acronym meaning Sound Naviagation And Ranging. It pretty much works on the echo principle. We all know that sound gets reflected from surfaces, resulting in echoes, but what is interesting is that the reflected sound carries much of the information about the surface from where it gets reflected. If one sends sound waves to the bottom of the sea, and analyses the reflected sounds coming back, one can make a fairly good idea of what is lying there. Thus any aeroplane debris collected at the bottom may be quickly and painlessly visualized.

One of the variants of sonar system used for such visualizations is Towed side scan sonars. These sonars have two sound emitting devices (technically known as transducers), one installed on each side of a towed body commonly referred to as a “fish”. Sound is sent down from each device and the resulting echoes recorded. A composite image is formed from both the echoes. This image can show all the debris lying at the bottom of the sea. Figure 3 here shows a typical sonar system employed for such works (Editor: Please reproduce figure 3.jpg here. Caption to be used: General view of a towed side scan sonar system showing the graphic recorder, shallow water tow cable, and two tow fish). This method of visualizing debris is far superior than the conventional means such as discovery by divers and manned submersibles.

Another newly used technique is the use of Remote Operated Vehicle or ROV (Editor please reproduce fig 4.jpg here). These are essentially robot vehicles that are sent to the bottom of the sea. These vehicles have video cameras and other sophisticated attachments over them with which the debris can be easily viewed. This technique is much safer than actual manned diving operations.

Finally a very sophisticated technique that has come into use only recently. It is known as GPS or the Global Positioning System (Editor please reproduce figure 5.jpg here). GPS is a portable, satellite based radio navigation system. An individual with a GPS receiver can instantly determine his or her precise location, elevation, speed and heading from information transmitted from orbitting satellites. This system was built by the United States Department of Defense for military positioning. Russian Federation of States uses a similar system known as Global Navigation Satellite System (GLONASS). However GPS is more popular and more widely used.

GPS has been used for locating aircraft debris in an interesting way. An investigator in a hostile or otherwise difficult terrain can use the GPS to know where exactly he is. Thus there is no danger of him getting lost, and he can cover wide areas ranging into tens of miles. GPS receivers can be hooked upto portable computers and all the recovered debris can easily be recorded directly into computers.

This is just a glimpse of how highly technical our crime investigation has become. Undoubtedly latest books in this field are keeping us informed of these developments. Professionals looking for more info can consult the book mentioned above.

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(Dr. Anil Aggrawal is a professor of Forensic Medicine at the Maulana Azad Medical College, New Delhi-110002. His E-mail is dr_anil@hotmail.com and his Website address is:

http://members.tripod.com/~Prof_Anil_Aggrawal/index.htm)

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(Note to the Editor: All figures in the article have to be taken from the accompanying floppy.)

Dr. Anil Aggrawal, M.D.

Professor of Forensic Medicine

Maulana Azad Medical College

New Delhi‑110002