Unidentified persons torched a Kerala State Transport Corporation bus after tying the hands of the driver, who was sleeping, to the seat at Poovar near here on Sunday, police said. The driver, Vijayambararaj, however, managed to get out from the parked bus. He suffered serious burns, police said. Police suspect that a gang pilfering diesel from parked vehicles could be behind the crime. The rear part of the bus was gutted.