Schoolboy Kriss Donald was still alive when he was set on fire in racist murder
Forensic scientist Ruth Ramage, 43, said he may have tried to extinguish the flames by rolling in mud on the Clyde walkway in Glasgow.
The 15-year-old's body was found by the walkway, near London Road on 16 March 2004, a day after he disappeared.
At the High Court in Edinburgh Mohammed Faisal Mushtaq, 27, Zeeshan Shahid, 28, and his brother Imran Shahid 29, deny racially aggravated murder.
Ms Ramage was called to the Clyde walkway and described her findings to the court.
"A smell of petrol was noted, particularly when the deceased was turned over onto his back," she said.
She said there were a number of stab wounds on his back and blood stains and scorch marks to logs about 50 yards away.
His body was also heavily stained with soil on top of the burn marks.
Advocate depute Mark Stewart QC, prosecuting, asked Ms Ramage about the significance of burned debris found between the logs and the place where the body was found.
She said: "In my opinion he was still alive when he was burning and had made his way down the grass to where he finally lay.
"He may have tried to extinguish the flames by rolling in the mud."
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