If someone were alive, Dr Feeney said a pathologist would find thick, black soot deposited through the airways and there would be a high level of carbon monoxide detected in the blood sample.
In this case, there was a carbon monoxide level of 5 per cent saturation.
Mr Battelage's body had areas where skin had been burnt and where it had been burnt away exposing soft tissue, charred bone and organs.
Once the body was turned over, to be removed, on the remains of a sofa bed, Dr Feeney said there was a strong smell of petrol.
She said the body had been found with fabric wrapped around the neck and lower head.
The cloth had preserved the skin beneath it which made it easier to see the injuries.
Of the six stab wounds, Dr Feeney said the most serious one was the long ``incised'' or cutting wound to the front of the neck, which went through the larynx and both the jugular vein and carotid artery.
She said it would have caused extensive bleeding and rapid blood loss, and death would have taken place within minutes.
Mr Battelage's hands and lower forearms, shins and knees had been burnt away and were not recovered or identified.
Justice Christian Whata urged the jury to put their emotions aside as they viewed the autopsy photographs.
Alahakoon is also charged with assaulting a woman, who has name suppression, with a pair of scissors on December 5, 2011, and again on Boxing Day that year.
The trial, before Justice Christian Whata, continues.