They recalled their final memories of the 16-year-old, who rode his bicycle to get McDonald's for dinner, only to be beaten in a dilapidated house in Fairfield East.

His mother and father appeared unable to look in the direction of Aymen Terkmani as he sat expressionless in the dock, accused of murdering and sexually assaulting Mahmoud on May 16, 2015.

A jury of seven men and five women found Terkmani guilty on Monday. The court was silent as the verdict was announced by a female juror.

His three-week trial heard Mahmoud's parents called him when he didn't return home from dinner after 9pm, and his hushed and slow voice caused alarm.

One of the last things the teenager whispered to his mother was: "I'm with my friend Aymen, come and pick me up."

Azzam Hrouk and Maha Dunia described searching for their son at his friends' houses, calling out his name in dark Fairfield streets, and asking to see CCTV footage at McDonald's in Villawood for any trace of Mahmoud.

Mr Hrouk confronted Terkmani on his front lawn at 4am, unaware he was speaking to his son's murderer as the teenager lay dead in the empty public housing property nearby.

"[Terkmani] raised his voice and said, 'So what do you want?' " Mr Hrouk told the court.

"He said, 'I know nothing, I just returned home.' He said, 'Are you interrogating me?' "

Later, a friend pointed Mr Hrouk to the vacant house on Belmore Street, where Terkmani and neighbourhood children gathered, played pool and smoked marijuana.

"I knocked on the door. I had no idea if Mahmoud was there or not."

Early the next morning, the teenager's body was found in a hallway of the house in a pool of blood. He had been beaten with implements such as a toaster and rolling pin, and sexually assaulted.

Mahmoud's body was riddled with injuries, including a skull fracture, traumatic brain damage and a collapsed lung.

Ms Dunia described her fears for her son when he did not return home earlier that evening.

"I was doing vine leaves to cook for Sunday for our family dinner and later on [my husband] asked me to call him," Ms Dunia said.

"I told [Mahmoud] to come home and he said 'Mum, it's all right I'm with my friend. I will come home on my push bike'. I said 'You better come home now.' "

In a later call, her son whispered a street name, before the line cut out.

The last time Ms Dunia saw her son alive was at sunrise that morning.

Mahmoud was working as a labourer six days a week, and always got up before dawn.

That morning he asked his mother if she needed anything before he left for work.

"I said 'No, God bless you,' " Ms Dunia said, through tears.