The teenage brother of Andrew Morton has recalled how the toddler was shot in the head as he held him in his arms.
Andrew Morton had wanted to watch fire engines
Brian McMillan, 13, said he and Andrew were on their way to a chip shop with a friend when they stopped to watch fire engines near their Glasgow home.
The youngster told the High Court in Glasgow that he heard a "pop" and then noticed blood was coming from the back of two-year-old Andrew's head.
Mark Bonini, 27, denies murdering Andrew in Cambusdoon Road on 2 March.
The Crown has rejected his plea of guilty to culpable homicide and is seeking a conviction on the murder charge.
Mr Bonini denies a total of 16 charges, including a string of alleged air rifle assaults over a four-week period.
Giving evidence via a video link on Thursday, the court was told that the teenage witness's brother had wanted to watch the fire engines.
"He was pointing and going: 'Fire brigade, fire.' He had wee toys of fire brigades.
"We went up to watch them. He was still in my arms but he was turned around to look at the fire brigade.
"All we heard was a pop. Andrew touched the back of his head and there was blood coming out," the court was told.
Brian Kerr, a 15-year-old friend of Brian McMillan, also gave evidence through a CCTV link.
He said Brian had been carrying his brother in his arms, with the child's head on his shoulder.
'Covered in blood'
"I heard a loud popping, like chewing gum popping when you blow a bubble," he said.
"Andrew put his hand to the side of his head and said: 'Ouch'."
Brian said that when Andrew's brother put his hand onto the toddler's head and took it away it was "covered in blood".
He told the court that his first thought was that the toddler had been shot by an air rifle.
He said the youngster had a hole "on the right side of his head, behind his ear".
The trial also heard from Christopher Queen, 22, who was in Mr Bonini's flat at the time of the shooting.
He told the court that the accused said "this is where I shoot the school children in the morning" as he opened the bedroom window.
Asked how he felt, Mr Queen said he had been really scared.
The trial continues.