The Bengaluru and Boston blasts have proved how it is almost impossible for even the best intelligence agencies to detect and prevent terror attacks. In Bengaluru, eight of the 16 injured were police personnel.

The CCTV cameras in Bengaluru showed how easily a person could park a stolen bike containing explosives next to a police vehicle without arousing any suspicion. In Boston, the perpetrators carried around pressure cookers and ball bearings without being suspected.
In such highly asymmetric warfare situations, the advantage lies overwhelmingly with the attackers. The Bengaluru and Boston blasts could have been carried out by three to four terrorists, but would require hundreds of police personnel to thwart them. The costs involved are also highly disproportionate — the Improvised Explosive Devices (IEDs) used in Bengaluru and Boston could be manufactured for a few thousand rupees, but it would require several crores to detect and defuse them.
It is difficult to detect the manufacturing of IEDs, since all the components — explosives, detonators, trigger circuits, power supplies, timers, etc. — can be assembled from readily available sources without arousing suspicion.
Batteries (AA, AAA, 9V) provide the power supply. The trigger circuits can be cellular phones, transistor radios, remote-controlled toys, etc. The timers are quartz circuit watches or mechanical clocks. The electrical ends of the receiver circuit (cellphone, remote-control led toy, radio, cordless phone, etc.) are placed inside the plastic explosive or detonating cap. The terrorist, who may be located several kilometres away, pushes a button on the transmitter circuit (cellphone, control unit of a remote controlled-toy, etc.) to send the signal to the receiving device, which detonates the explosive.
Apart from the readily available ammonium nitrate and fuel oil (they are sold in agricultural markets), other plastic explosives such as RDX (Research Department eXplosive, chemically cyclo-tri-methylene-tri-nitro-amine), PETN (Penta-Erythritol Tetra-Nitrate), Semtex (a mixture of RDX and PETN) etc. can be made in cottage factories from easily sourced raw materials.
RDX is manufactured by reacting concentrated nitric acid (available in every school laboratory) with hexamine. Hexamine is widely used as a medicine as well as an industrial chemical. Hexamine can be prepared in one’s kitchen by reacting two common chemicals — formaldehyde and ammonia. Purchasing large quantities of hexamine would not arouse any suspicion since it is used as an antibiotic for treating urinary tract infections, for preservation of cheese, as well as in brake and clutch linings, fireproof materials, rubber and textile adhesives, in paints and lacquers, in the photographic industry, as a corrosion inhibitor, as a protein modifier, and in the production of deodorants and hair-fixers.
PETN, which is a very powerful explosive, is even more easily available since it is used as a heart medicine. The vasodilator Lentonitrat is almost pure PETN. Less than one kilogram would be required to bring down an airliner. All one needs to do is to buy a kilo of Lentonitrat from a medical supplier, and install detonators and trigger circuits.
Plastic explosives are almost impossible to detect in the field by any practical means. Metal detectors do not pick them up. If they are made by an expert, they are odourless, look like children’s plasticine, and can be moulded into any shape so that they can be hidden deep within crevices. Even if they have been made in a makeshift laboratory, they have the odour of vegetable oils or fruit essences. Even highly trained sniffer dogs have had very limited success in differentiating them from food products.
Tests which can detect the chemicals involved in plastic explosives, like Neutron Activation Analysis, Gamma Ray Irradiation and Laser Spectroscopy, require equipment costing millions of dollars. They also require one to go very close to the suspected explosive, which is what one never wants to do. These equipment can at best be used at entrances of airports or VIP security zones.
The combination of ammonium nitrate/fuel oil mixture (ANFO) has also been used in several recent attacks in India. Ammonium nitrate is widely used as an agricultural fertiliser. The fuel oil can be diesel, kerosene or molasses. ANFO is widely used in India and abroad in mining, quarrying and civil construction. It is practically impossible to control the sale of ANFO or keep tabs on buyers.
Preventing IEDs from exploding is also difficult. VIP zones and motor convoys are protected against Remote-Controlled IEDs (RCIEDs) by the use of electromagnetic jammers. These jammers emit high-power radio waves. If they are of higher power than the signals transmitted by the terrorist, they either jam or prematurely detonate the IED. But the use of jammers causes a lot of trouble to the general public. If a terrorist brought an RCIED within range of a jammer, the RCIED could explode instantly. While the VIPs would be saved, there could be many more civilian casualties in the streets outside. Also, since the best jammers work over the entire frequency range of 20 Hertz to 2,000 MegaHertz, they would interfere with cellular phones, television and radio reception. The general public would not put up with the prolonged inconvenience of being without TV, radio and telephones.
It is almost impossible for even the best intelligence agencies to detect and prevent such terror attacks. So stop the political blame games and focus on increased surveillance and policing at the street level.

The writer heads a group on C4ISRT (Command, Control, Communications and Computers Intelligence, Surveillance, Reconnaissance and Targeting)