Teen killed so he wouldn't snitch: witness

Yigit Can Erdogan, known as John, has pleaded not guilty to murder and detaining a person in company to gain an advantage in a Supreme Court trial.

The 22-year-old is accused of orchestrating the torture and murder of a teen in 2019 over allegedly stolen property.

The body of the 17-year-old was found in a shallow grave in the Blue Mountains, wrapped in plastic and tape, eight days after he was last seen by his family.

The prosecutor says he was found naked bar his underwear, with 25 stab wounds to his neck, a fractured skull and bleeding to the brain.

He had been detained, threatened and hit by Erdogan on March 12, 2019, Ken McKay said when opening the crown case, before he was forced into a car with a group and driven around in an attempt to obtain money from people who knew him.

On Wednesday a witness who was present for parts of the ordeal told the court what he remembered after the group returned to the house.

The witness - who cannot be identified - says he saw teen sitting in the hallway, stripped down to his underwear, before he left the room.

"He still looked distressed," the man said.

"I also had been distressed by what was happening."

Some time later, Erdogan found the man and told him to soundproof the house and close the blinds.

He did so, before again excusing himself to another part of the house and putting on headphones.

"The next thing I remember ... John had opened the door ... and he had said, 'This kid is so injured that if we take him to a hospital he is going to snitch. We need to kill him'," the man told the court.

"Not long after - I could hear it over my own headphones - there was very loud banging multiple times."

When he next emerged, the man said he saw a large mound of paper towels, with the victim's legs sticking out from underneath them.

They were covered in cuts, he said.

"I heard ... 'Let the body sit, to let the blood drain out'."

Erdogan twice aggressively demanded the witness hand over his phone, which he did.

The man then helped clean up the house.

"I assisted with mopping up the blood using a floor squeegee."

"I recall that there was also rubbish bags being used which ... all the soaked paper towels were being thrown into.

"I do also recall (someone) picking up... what I assumed was some bodily tissue from (the victim)."

The man recalled seeing steel capped boots discoloured with what he assumed was blood, and the handle of a knife - no blade - on the dining table.

The teen's body was wrapped in a tarp and duct tape, and placed in the boot of a car.

The witness and one other then travelled to the Blue Mountains to bury the body, stopping at McDonalds for a drink on the way back.

About five days later the man went to the police, telling them about several items belonging to the teen that remained in the house, as well as instruments used to clean up after his death.

The witness has escaped charge.

Erdogan admits participating in some of the early parts of the alleged saga and the clean-up, his lawyer told the court earlier this week, but he disputes "anything in the middle".

The trial continues.

Australian Associated Press