A senior forensic scientist, who was part of the team that collected burnt articles from the bogie, said "they had found fire cracker material from the bogie which indicates that burning of crackers rapidly spread the fire in the bogie, however, initiation of fire is still not known."
The fire crackers or its powder seems to have been stored below at least six seats in the coach, he said.
The team of Andhra Pradesh Forensic Science Laboratory (APFSL) experts, who examined the gutted S-11 bogie of Tamil Nadu Express, submitted a report in this regard to the Railway authorities yesterday, the official said, adding that a copy was also forwarded to Commissioner, Railway Safety (South Central circle).
Thirty-two passengers were charred to death and 25 others injured when a fire broke out in S-11 coach of the New Delhi-Chennai Tamil Nadu Express on July 30 near Nellore district of Andhra Pradesh.
A "blast theory" and short-circuit behind the devastating fire had initially made the rounds as one injured passenger, Madanlal, had earlier claimed that he woke up after hearing a loud noise (with sound just like a blast) in the coach and that there were at least two more such thuds.
Railway Minister Mukul Roy had earlier entrusted the investigation in the mishap to D K Singh, the South Central Railway Safety Commissioner.