“From our investigation, the motive behind the mischief was due to a misunderstanding after the suspects and some tahfiz students mocked each other a few days before the fire,” Singh said at a televised news conference Saturday.

Singh said six of the seven suspects tested positive for drugs. Two of them had been detained before, one on charges of vehicle theft, another for rioting, he said.

Singh said the boys could face murder charges.

Police identified the suspects after viewing security cameras from an adjacent building.

Firefighters and witnesses have described scenes of horror – first of boys screaming for help behind barred windows as neighbours watched helplessly, and later of burned bodies huddled in corners of the room.

Officials initially said they suspected the fire was caused by an electrical short-circuit but later said this wasn’t the case.

The charred bodies were released Friday to family members after being identified through DNA testing and buried the same day.

The dead are 21 students aged between six and 16 and two teachers in their 20s. The death toll from the fire has sparked outrage over inadequate safety measures at the school.

There have been 211 fires involving similar religious schools since 2015 in the country.

In the deadliest such fire, 27 female students of a religious school in northern Kedah state died in 1989 when fire tore through the school and eight wooden hostels.

Kyodo, Associated Press, Agence France-Presse