A charred iron container that police found about a foot from where a basket of fruits lay strewn after the explosion outside Basanti Sweets in Nagerbazar on Tuesday morning is suspected to be the “bomb” that killed a child and injured many.

The container’s lid had been blown off but it didn’t disintegrate like a tiffin box would have under the impact of explosives.

Investigators said they couldn’t immediately figure out how the explosion was triggered. There are multiple possibilities to consider before arriving at a hypothesis, according to police and explosives experts.

• A thread with one end jutting out of the device could have been used to ignite the explosive device like firecrackers. If this mechanism is employed, the timing of the explosion can be delayed or shortened by using a long or shorter thread.
  
• Another way of triggering an explosive device is by applying pressure on it. Landmines go off when this happens.
  
• The presence of a timer and a circuit inside the device can turn it into a bomb that can be auto-timed or controlled with an external device.
  
• A detonator can be manually used to set off an explosive device.
  

While all of the mentioned methods can work as a trigger, the quantity of explosives stuffed into a device and their properties determine how powerful a blast is.

In Nagerbazar, investigators hadn’t found any evidence until evening of a timer or a circuit being used. “Had that bomb been manually detonated, the person handling it would have been injured as well. Since that did not happen, we are left with two options to deduce — either the explosion was triggered by a thread or by pressure,” a police officer said. “By visually examining the remains of the device, it is difficult to guess the

exact nature of the explosion. Things will be clearer in the forensic laboratory.”

The explosives stuffed inside the container had traces of ammonium nitrate, glycerine and sugar, according to the police.

This is a combination that can cause high-intensity blasts. A few oval iron balls (used in fishing nets), some stone chips and sand were found strewn at the blast site, suggesting that these were used as shrapnel. But since their quantity was less, the impact was restricted to a small radius, the police said.

The bottom portion of a storeroom shutter was blown off but there were no holes or perforations. The police have inferred that the explosives used weren’t very strong and their quantity wasn’t much.

A CID officer said the explosive device had the features of a crude bomb stuffed with ammonium nitrate as well as an improvised explosive device filled with compounds of nitro-glycerine.