Three students are in custody in southern Uganda on suspicion of starting a school dormitory fire that killed at least nine children and injured 40.
The three had recently been suspended for bringing alcohol into St Bernard Secondary School in Rakai, police say.
The dormitory's doors were padlocked at the time of the fire, trapping dozens of students inside.
Some of the bodies were burned beyond recognition.
Police used DNA to identify remains. Thirty pupils were taken to hospital.
Six alleged accomplices of those who were arrested are still being sought.
The Ugandan Red Cross said its team had managed to break the padlocks using a hoe and rescue many of those trapped.
"We are happy to have managed to save many who escaped with burns but at least did not die," Irene Nakasiita, communications co-ordinator for the Uganda Red Cross Society told the BBC.
She urged schools to boost student safety by ensuring fire extinguishers were available, and that pupils knew how to use them.
Henry Nsubuga, the headmaster, described the fire, which took hold in the early hours of Monday, as a "heinous act".
Gerald Karasira, a local councillor, said people living nearby desperately tried to put the fire out using sand, water and bricks but rescue efforts were complicated by the locked doors and heavy smoke inside the property.
"Had the firefighting truck been near within the district, maybe we would have saved lives and property," he is quoted as saying by New Vision newspaper.
Rakai district is located is about 192km (119 miles) south of Kampala, near the country's border with Tanzania.
A number of senior government officials, including the education and security ministers, have been visiting the scene.
Damage done by school dormitory fires is usually aggravated by overcrowding, which hampers rescue efforts, the BBC's Patience Atuhaire reports from the capital, Kampala.
In 2008, a dormitory fire at a primary school near Kampala killed 20 pupils.
A wave of school fires followed shortly after that, but they have been fewer in recent years, our correspondent adds.