A 22-year-old man has been charged with the sexual assault and murder of Sydney teenager Mahmoud Hrouk.

Mahmoud's badly beaten body was found by his family in a home in Fairfield East in May.

Police arrested the 22-year-old Fairfield East man at 3:00pm on Thursday and charged him with murder and aggravated sexual assault.

He was refused bail to appear at Fairfield Local Court on Friday.

Mahmoud was last seen on the evening on Saturday, May 16, when he rode his bike to a McDonald's outlet in Villawood.

When he did not return home, his family started a search.

The following day Mahmoud's parents discovered his bloodied body when they looked through the window of an abandoned home on Belmore Street in Fairfield East.

His bike was found about 200 metres from the home.

Police said the former Granville Boys High student had been brutally bashed and had serious head injuries.

Detective Inspector Grant Taylor earlier described the vacant house where the boy's body was found as a "shocking crime scene".

"As far as crime scenes go this was an appalling scene to attend and something that remains very vivid in the memory of emergency services workers who attend those types of events," he said.

Detective Inspector Taylor said the brutal sexual assault Mahmoud Hrouk endured was "part of the reason he died".

He said the 16-year-old was held in the vacant house before he was killed.

"We believe he was kept there against his will and this is when he was sexually assaulted," Detective Inspector Taylor said.

He said the house where Mahmoud had been murdered had been used by local teenagers in the months leading up to the death.

Detective Inspector Taylor said Mahmoud was not known to police.

"Mahmoud was a hard-working boy from a loving family; we found nothing to suggest he was up to anything bad. He was just going about his daily life," he said.