JINAN -- A fatal school bus fire that killed 11 children and two adults in eastern China's Shandong province on May 9 was allegedly started by the bus driver, who also died, police said Friday.

The 11 children were aged between three and six, with five from the Republic of Korea and the rest from China.

The fire was started on the bus floor near the driver's seat. A lighter cap was discovered nearby and gasoline residue found on multiple spots on the bus, according to a police officer with the Shandong provincial public security bureau.

Electricity faults and traffic accidents were ruled out as the cause of the fire, the police officer said.

The driver's overtime and night shift allowance had been suspended, angering him, causing him to buy gasoline to set the fire, police said.8 Police received reports around 9 a.m. on May 9 about the fire inside Taojiakuang tunnel in Huancui district, Weihai city. The rented bus was delivering the children to a kindergarten, with 13 people onboard.

All were killed, including a female teacher.