Perak Criminal Investigation Department chief Senior Asst Comm Yahya Abd Rahman said investigations found that there were lots of traces of gunpowder at the premises in Jelapang Maju Industrial Area, near here.
However, the police have yet to determine what ignited the fireworks and caused an explosion during the 1.55pm incident on Tuesday (Dec 11).
Six people, including the shop owner and five teenagers, were killed during the incident.
SAC Yahya said all six died from 80 to 90% burns to their bodies.
He said the police have also interviewed one of the survivors from the incident.
"The survivor, in his 50s, works as a driver for the company," he told a press conference at the Raja Permaisuri Bainun Hospital mortuary yesterday (Dec 11).
"We have also viewed the CCTV recordings at the shop," he said.
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