The driver of the bus that caught fire and left 26 people dead in Taiwan on Tuesday might have gone into coma after inhaling poisonous smoke, said prosecutors in Taoyuan district.

According to local media reports, the post mortem showed that the driver's respiratory tract was burnt and choked, a sign that he possibly inhaled high temperature smoke, prosecutors said.

They said the driver was possibly poisoned by carbon monoxide and fell into coma and lost control of the bus.

Some eyewitnesses have claimed that the bus kept going for 1,000 meters after catching fire and the driver did not open the emergency exits in time. They said he should have survived since the emergency exit was near his seat.

Prosecutors have sent samples of the driver's remains to forensic experts to find if he had poor health or was on alcohol or drugs.

The fire began from the front part of the vehicle, and prosecutors found that the wires got mixed up at some point, possibly due to overload.

Some have speculated that the short circuit was caused by the water dispenser and Karaoke equipment near the driver's seat.

Prosecutors combed through the vehicle to see if there were some other flammable things at the front of the bus, such as cigarette butts in the trash can or on the ground, pesticides or wine near the driver's seat.

One of the major reasons for the?heavy casualties was that the left rear emergency exit did not open. The investigators found that the exit had a built-in lock system that should not have been there.

They also discovered similar built-in lock system at another bus of the same type from the same company. Prosecutors said they would further investigate the buses.