Ten people being held in connection with a fire that killed 19 Ugandan schoolgirls are all school employees, a senior police official said Saturday.

Nine guards and a matron are being held on suspicion of negligence, said the officer, who asked for anonymity because he was not authorized to comment on an ongoing investigation.

The officer said police suspect that Monday’s fire at Budo junior school was started by arsonists. Witnesses reported a loud bang as the building burst into flames. The doors to the dormitory had been locked from outside.

Young survivors spoke of struggling to climb through tiny windows as their sleeping quarters filled with smoke.

Police are following two leads involving disgruntled school staff, the officer said. They have offered $3,000 for information.

The fire was the third fatal school fire in Uganda in two years.