Use what you can procure easily without attracting suspicion. Avoid fancy things that will attract attention to you.
That is the instruction imparted by Al Qaeda [Images] and other Pakistan-based terrorist organisations to their trainees. Even before Al Qaeda started imparting this instruction, Palestinian terrorists had been following this dictum on their own.

Till the early 1980s, Palestinian and ideological terrorist groups had  a fascination for sophisticated explosives such as RDX and other military-grade explosives and semtex, an explosive made by a factory in the then Communist Czechoslovakia, which had a very weak vapour density, thereby making it difficult for dogs to detect its presence.

The action taken by the security agencies of the world to make it difficult for the terrorists to procure them made the terrorists turn to nitrogenous fertilisers, which were easy to procure without creating suspicion. The first major instance of the use of fertilisers was the unsuccessful attempt made by Ramzi Yousef of Pakistan and some of his associates to blow up the New York World Centre in February 1993. They drove into the garage of the WTC a truck loaded with about 1,500 pounds of urea nitrate  and hydrogen cylinders and tried to cause an explosion. The attempt was not very successful. It killed six persons and caused some damage. Investigation revealed that Ramzi and his associates had learnt this modus operandi in Pakistan.

In 1994, an unidentified group of Palestinians had planned to blow up the Israeli diplomatic mission in Bangkok by using a truck filled with nitrogenous fertilisers. The truck broke down near a traffic signal, so they abandoned it and ran away.
In 1995, Timothy J McVeigh, an American national not belonging to any terrorist organisation, blew up the federal office building in Oklahoma City with a truck bomb carrying a mix of 5,000 pounds of fuel oil and fertiliser, killing 168 people.
Following this, security agencies in many countries started closely monitoring the purchase of nitrogenous fertilisers in large quantities by persons who are not farmers. Some countries also made a police permit necessary for the purchase of large quantities of fertilisers. All sellers of fertilisers were advised to look out for suspicious transactions and immediately alert the police.

In 2003, a suspected sleeper cell of Al Qaeda in the UK reportedly purchased 1200 pounds of fertilisers from a shop. The seller did not alert the police. However, the owner of the warehouse where the cell had kept the fertilisers got suspicious and alerted the police, who arrested the cell members. Since then, fertiliser manufacturers in Western countries have reduced the percentage of ammonium nitrate, which is used for bomb-making, in the fertilisers manufactured by them. In May 2006, the Canadian police arrested a group of Pakistanis and others who were planning to cause an explosion by using nitrogenous fertilisers.

Since then, instances of the use of nitrogenous fertilisers by terrorist groups has come down in Western countries, but have increased in India. In many of the explosions caused by jihadi terrorists in different parts of India since 2004, the material consisted of a mix of ammonium nitrate and fuel oil. It was this mix which was reportedly used in the explosions in Mumbai's suburban trains in July 2006, and in the subsequent serial blasts in UP, Jaipur [Images], Bengaluru [Images] and Ahmedabad [Images].

After the police and security agencies in the West started monitoring the sale and purchase of nitrogenous fertilisers, Al Qaeda and other jihadi organisations in Pakistan started advising trainees in their camps to use incendiary devices instead. These consisted of gas cylinders and other inflammable material such as gasoline. On August 3, 2004, the British police arrested Dhiren Barot, also known as Bilal al-Hindi, on the charge of helping the Al Qaeda. He has since been convicted by a British court and jailed for 30 years. He is a Gujarati Hindu migrant from East Africa who had embraced Islam.

Lecture notes recovered from his possession reportedly said inter alia: 'Make use of that which is available at your disposal and bend it to suit your needs.' He claimed to have learnt this in a training camp in Pakistan. He advocated the use of incendiary devices instead of explosive devices.

Such incendiary devices were used in the terrorist attack on Samjhauta Express near Delhi [Images] on February 18, 2007. A car with gas cylinders was also sought to be used by Kafeel Ahmed, an Indian from Karnataka, when he along with an Arab accomplice tried to blow up Glasgow airport in the UK on June 30, 2007. The attempt failed, but he died of burns.

For causing explosions, terrorists have now been increasingly using peroxide-based liquids which could be converted into an explosive material. Many articles of common use such as certain items of cosmetics and cleaning solutions have a peroxide component. It is easy to procure them in any supermarket or drugstore without causing suspicion. It is difficult to detect. They could be easily carried into an aircraft and other modes of transport. They are light and easy to carry on one's person. They are cheap and affordable for terrorists who do not have much funds at their disposal. Whereas an ammonium nitrate-fuel oil IED may cost around US $ 60 or more, a peroxide-based one could cost  around US $ 25 or even less.

The peroxide-based improvised explosive devices used by the four suicide bombers -- three of them of Pakistani origin trained in a terrorist training camp in Pakistan's tribal belt -- for their attack on London's transportation system on July 7, 2005, attracted much attention and comment, but that was not the first time it was used. Palestinian terrorists were the first to have used a peroxide-based IED in Israel, in 1980. It was used for the first time outside Israel in London [Images] by Palestinian terrorists in 1994 in an attempted attack on the local Israeli embassy.

In 1995, Ramzi Yousef, then living secretly in Manila after his involvement in the explosion in the New York World Trade Centre in February 1993, had planned to use it for blowing up a number of flights originating from South-East Asia. An accidental fire in his apartment, where he had kept some liquid, alerted the Manila police, and he ran away to Pakistan where he was subsequently arrested and handed over to the US.

Peroxide-based explosives were reported to have been used by Al Qaeda in some of its post-9/11 terrorist strikes in Bali, Casablanca and Istanbul.

While the use of the peroxide-based IED by the suicide bombers on July 7, 2005, was devastatingly successful, a similar use attempted by another group in London on July 21, 2005, was not. The bombers of July 7, 2005, had prepared the peroxide-based explosive in the bathtub of a flat used by them. Some quantity from that had remained unused which was sought to be used by the bombers of July 21, but the IEDs failed because the explosive material had disintegrated.

The use of peroxide-based liquids for fabricating an explosive material has two drawbacks. First, they can accidentally cause an explosion or a fire while the explosive material is being prepared from the peroxide-based liquid, thereby killing the bomber or alerting the police. Second, they quickly disintegrate if not used immediately after fabrication. Whereas ammonium nitrate -based explosives can be kept stored for days and even months without disintegration, one cannot similarly store peroxide-based  explosive material.

In August 2006, the London police discovered a plot by a group of terrorists, many of them Pakistanis, to blow up a number of US-bound planes by taking liquids capable of being converted into explosives into the aircraft and fabricating the explosive inside the aircraft. The Pakistani authorities arrested Rashid Rauf, a British resident of Pakistani (Mirpuri) origin, on suspicion and found in his possession some bottles of hydrogen peroxide liquid. He claimed that he had bought them in a drugstore for use as an injury disinfectant. Investigation revealed that he was related by marriage to Maulana Masood Azhar, amir of the Jaish-e-Mohammad. His interrogation also allegedly gave the tip-off regarding the London plot. He managed to escape from custody while being tried before a Pakistani anti-terrorism court. He is still absconding.

Peroxide-based liquid explosives lend themselves to easy use for acts of suicide terrorism. Peroxide-based explosives were reported to have been used in many of the suicide attacks in Pakistan last year after the commando action in Lal Masjid.
In its issue of August 19, 2008, The Times of India, Ahmedabad, reports: 'The Students Islamic Movement of India has been experimenting with a new concoction  using hydrogen peroxide to make liquid bombs. Prototypes of liquid bombs were first experimented in Vagamon hill resort in Kerala [Images] where a SIMI [Images] camp was held in December 2007 to impart terror training to its cadres. The camp was organised by Kerala SIMI secretary P A Shivli. Experiments with hydrogen peroxide were revealed in the statement of SIMI general  secretary Safdar Nagori during interrogation after his arrest by the Indore police on March 26 this year.'

The SIMI terrorists arrested by the Gujarat police had planted over 10 IEDs with ammonium nitrate and mechanical timers in Ahmedabad which exploded on July 26 causing death and destruction. They had also planted 25 IEDs with integrated circuits in Surat [Images] all of which failed to explode. A question was raised whether a 100 per cent failure of 25 IEDs was possible. The Gujarat police have not given any reasons for this failure so far.

While they have revealed that the Ahmedabad IEDs had ammonium nitrate and fuel oil, they have not said what was the explosive material in the Surat IEDs. If the terrorists had experimented with a peroxide-based explosive in Surat, a 100 per cent failure is possible due to the disintegration of the explosive material if it had been fabricated much in advance and kept in storage. That is what happened in London on July 21, 2005.

(The writer is Additional Secretary (retired), Cabinet Secretariat, Government of India, New Delhi, and, presently, Director, Institute For Topical Studies, Chennai. E-mail: seventyone2@gmail.com)