Salim Hamzy, 18, and his father Toufik Hamzy, 64, were shot dead as they sat parked in a ute at Guildford at 9am on October 20.

Strike Force Ormerod was established to investigate the killings amid speculation the men were victims of the tit-for-tat gangland war between the Hamzy and Alameddine crime networks in their battle over drugs.

Investigators have since seized two cars - a grey Ford Mustang and a burnt-out Lexus SUV - both believed to have been used as getaway vehicles in the murder.

Police revealed on Tuesday that two people have been charged with offences related to Strike Force Ormerod.

A 25-year-old man was charged last month with accessory after the fact to murder and refused bail.

He will appear at Parramatta Local Court on September 8.

Detectives also charged a teenager last month after seizing a gel blaster from a Merrylands West home.

A 17-year-old boy was charged with possessing an unauthorised prohibited firearm, not keeping a firearm safely and possessing an unregistered firearm.

He will appear at a children's court on September 30.

Homicide Squad commander Danny Doherty appealed to anyone who may have seen the distinctive grey Ford Mustang or Lexus SUV prior to the murders.

"Following our last public appeal, detectives have since charged a man with accessory after the fact - this will not be the last arrest," Detective Superintendent Doherty said.

Police are also appealing for information into a suspicious disappearance and death of a man from Sydney's CBD earlier this year.

Hongli Qi, 28, was last seen by family at Sydney's Town Hall, about 1pm on may 11.

His body was found in bushland near Packer Road, Blaxlands Ridge, earlier this month.

His death is being investigated under Strike Force Procyon.

Australian Associated Press