A fire investigator did not see water from sprinkler systems around the Doha mall where 19 people, including three New Zealand children died, until the day after the fatal blaze.
The forensic expert from the Qatar Ministry of Interior was the author of an internal investigation report into the Villaggio Mall fire in the Gulf state capital last May.
He was the last witness to be called by the prosecution at a hearing in a Doha court to determine criminal responsibility for the deaths caused by the blaze.
Of the 19 people who died, 13 were children, including two-year-old New Zealand triplets Lillie, Jackson and Willsher Weekes, who were at the Gympanzee daycare centre.
The fire investigator was asked at the hearing overnight (NZT) whether the Villaggio and Gympanzee sprinkler systems and fire extinguishers were functioning.
He said he did not see water in or around the shops until the day after the blaze, when the sprinklers were turned on, Doha News reported.
The fire apparently started when flammable components inside a florescent lightbulb in a Nike shop came into contact with the hot plastic of the insulators within the device, he said.
A malfunction caused the temperature of the electric conductor to spike, burning the insulators, which fell in ashes on to boxes of sports equipment, igniting them.
Smoke containing toxic carbon monoxide quickly spread to neighbouring Gympanzee daycare centre.
A total of 31 shops were damaged.
The type of light bulb used had an aluminium coil inside rather than a more fire-resistant copper one. It was commonly found by fire experts to be a cause of fires in Qatar.
The hearing is due to resume on February 7 with the defence calling witnesses
At least some of the seven defendants - two Gympanzee co-owners, four representatives of Villaggio and an employee of the Ministry of Business and Trade - are expected to testify.