The deputy commissioner of police, detective department, Narayan Ghosh, said the explosive, initially thought to be RDX, was confirmed by explosive experts late last night as Amfo which is known to be close to TNT (tri-nitro-toluene) in its explosive capacity.

Ghosh said the black substance, packed in 25 transparent polythene bags, appeared very much like RDX at the first instance but tests by the Central forensic science laboratory proved otherwise.

Amfo is an equally powerful explosive capable of causing damage of equal extent when detonated, CSFL sources said adding the fertiliser ammonium nitrate is used as an amalgam compound with fuel oil to give it the required explosive nature.