Dhillon said he drove around aimlessly for at least three hours trying to decide what to do.

Over two months after toddler Gurshan Singh Channa's death shook the Indian community here, Victorian police on Monday cited heat exhaustion as the probable cause, as the boy was driven around in a dangerously high-temperature car boot for nearly three hours.

The accused, Gursewak Dhillon, confessed after his arrest that he disposed off Gurshan's body after carrying him around in the boot of his car, but denied having deliberately caused him harm.

Forensic tests carried out on a seized Commodore sedan showed that the temperature in the boot might have reached 50 degrees while Gurshan was being driven around the city on March 4, The Age said in a report on Monday.

Dhillon said the toddler was accidentally knocked down unconscious when he ran into the door at the house in David Street, Lalor. A post-mortem found slight bruises consistent with a minor knock to the head, but failed to find a cause of death.

Dhillon said he placed the boy in the car boot and drove off with the intention of going to a hospital. He said he panicked, fearing the authorities would find out that he had entered Australia under a false name and that he would face deportation.

Dhillon said he drove around aimlessly for at least three hours trying to decide what to do.

It is said that a passing woman motorist helped the accused in buying petrol from a service station when he ran out of fuel. He left the car with Gurshan still in the boot while the woman reportedly gave Dhillon a lift to a service station.

The woman is yet to come forward.

Detectives have now obtained closed-circuit security footage confirming that the accused was at a northwestern suburban service station making a purchase.

Dhillon finally dumped Gurshan's body by the roadside near Tullamarine airport at Oaklands Junction, more than 20 km from his home. The body was found nearly seven hours after the three-year-old was reported missing.

Dhillon has been charged with manslaughter by criminal negligence and is in custody until June 29.

Gurshan's parents, Harjit Singh and Harpreet Kaur Channa, have returned to India. — PTI