The fourth person charged over the alleged mistaken-identity kidnapping and murder of elderly grandfather Chris Baghsarian is also accused of arson.
Moustafa Ohrok, 19, did not apply for bail in Mt Druitt Local Court on Wednesday after being charged with the murder of the 85-year-old in February.
Ohrok was arrested on Tuesday, after Mr Baghsarian was taken from his home in Sydney's north in the early hours of February 13.
Three others have already been charged and remain before the courts.
NSW Police Commissioner Mal Lanyon said the young man arrested on Tuesday was involved in the initial abduction of Mr Baghsarian.
"We're alleging this 19-year-old actually provided a firearm that was used in his initial kidnapping," Mr Lanyon told 2GB radio.
Investigators are continuing to look into other possible suspects, he said.
Ohrok faced two separate charges in court on Tuesday of damaging property by fire and participating in a criminal group.
He will next face Parramatta Local Court on the arson matter on May 21.
The 19-year-old will appear in Penrith Local Court on the murder and kidnap charges on June 12.
The widower was not the intended target and had been taken in a case of mistaken identity, police have said.
They made several public appeals, urging the kidnappers to release the 85-year-old and return him to his family.
But on February 24, his body was found near a golf club in Pitt Town in Sydney's northwest.
Police suspect the perpetrators aimed to abduct a relative of Sydney businessman Dimitri Stepanyan, who lived on the same street as Mr Baghsarian, with the hope of receiving a $50 million ransom.
Investigators believe Mr Baghsarian was killed on the night of February 14 at a makeshift stronghold in Dural, about a half-hour drive from where his remains were found.
A growing number of underworld attacks have permeated Sydney streets, with Mr Lanyon saying the city is dealing with a very different organised crime environment.
"We are seeing young people predominantly being contracted online to conduct very serious criminal activity," he said.
"There are a lot of young people who are seeing what they believe to be an easy dollar but not understanding the ramifications ... the crime of murder carries life."
Five others, including a 15-year-old boy, were charged on Wednesday over a separate kidnapping in southwest Sydney.
The group are accused of beating up a bodyguard with a baseball bat and abducting him in his own car before being freed by police an hour later.
