Three persons were killed in the blast which destroyed ground floor and the first floor.
Prime accused Manohar Gurunani made loud-noise 'sutali bombs' in the shop using a newly-purchased machine, according to the police.
At a press conference on Friday afternoon, Nashik Police commissioner Vinod Lokhande said Gurnanai had earlier kept the machine at his Maratha Fireworks Factory at Rasegaon in Dindori taluka. But due to frequent power-cuts,
it was shifted here.
The firecracker powder contained potassium nitrate and other ingredients of sutali bomb, also popularly called 'atom bomb', he said.
Due to the small, closed room, impact of the blast increased, he said. No high-intensity explosives like gelatin were found.
Gurunani had a firecracker-manufacture license for Rasegaon factory, Lokhande said.
According to police, the shop is owned by Shakti Charandas Gavai, a local resident. He rented it out to Lalit Ramdas Page for manufacturing rangoli colours, but Page and Gurunani started manufacturing firecrackers there.
