Police inspect the blast site near the Richmond Town area in Bangalore on Friday. (Bangalore News Photo)

Bangalore, July 25: The Bangalore bombers tossed up a cocktail of low-intensity explosives and commonplace but lethal nuts and bolts to target India’s premier high-technology city.

The intensity of all explosions was low, according to Bangalore police commissioner Shankar Bidari.

Barring two explosive devices, which had ammonium nitrate, the others had low-grade chemicals. One of the bombs with ammonium nitrate, used in fertilisers, resulted in a fatality.

The extremists had packed the bombs with nuts and bolts that can kill and maim bystanders — the possible targets because most devices were kept near bus stops or on the edge of pavements. The bombs were concealed using tin sheets and buckets and had timers.

Nuts and bolts at a blast site. (Bangalore News Photo)

One explosive each was kept in front of a petrol pump on Raja Ram Mohan Roy Road and another in front of an electric transformer adjoining a sports goods shop on the Eagle Street-Hosur Road corner in Langford Town.

Investigators are now working on two theories — one that the explosives were kept after loosening the soil on footpaths the previous night. Second, two teams planted the bombs on one site after the other not long before the explosions took place.

A section of the police officers said overnight and morning rain might have dented the strike power of the bombs, explaining why the casualty was low despite the bombs being packed with nuts and bolts.

However, other police officers said they think the intention of the plotters was to demonstrate their ability to strike at will rather than to kill a large number of people.

These officers said the two-team theory appeared more strong. Police said the pattern becomes clear especially on Hosur Road as the first blast took place near a bus stop adjoining the St John’s hospital playground and hostel wall at 1.30pm.

After this, four more explosions took place on the same road — a distance of 4.5km to the last location on Raja Ram Mohan Roy Road — around 2.15pm.

The police are working on the premise that if one of the extremists got off a vehicle and placed the bomb and got back, the time taken from Madiwala to Raja Ram Mohan Roy Road would be around 35-40 minutes.

“They would have placed the explosive device, activated the timer and moved on from every location,” an officer said.

The second team could have planted three explosives within a distance of 2km on Mysore Road — first near the Gopalan Mall bus stop and another at Nayandahalli. The mall bomb went off at 5.30pm, much later than the one at Nayandahalli at 1.35pm.

The third device went off near RV Engineering College on Mysore Road. “The rain could have damaged the timers,” an officer said.