Sparos, who is in Lithgow jail serving 15 years for his involvement in the multi-million-dollar drug ring, was charged on Thursday with the murder of father-of-two Gemahl Maika in south-western Sydney in April 2011.

Mr Maika, 38, was shot 10 times by a lone gunman outside his home in Glen Alpine after he returned from a night-time TAFE class. His wife, Marama, a drug and alcohol counsellor, and his two daughters, aged 11 and 9, were inside the home at the time.

Mr Maika had been a witness in the case against the Golden Gun cocaine syndicate and police will allege that Sparos paid the alleged gunman, Maximillian Mazzilli to carry out the hit.

Sparos' wife, Christine Saliba, was also arrested on Thursday and charged with being an accessory before the fact to murder. The couple's charges followed the arrest of three men, including Mazzilli, 33, and former Commonwealth and world champion kickboxer, Adam Keith Watt, 46, on Wednesday.

Watt, who fought under the name "Aussie Sniper", was also charged with being an accessory before the fact to murder.

In evidence before Parramatta Local Court on Thursday, it is alleged that Mazzilli told an undercover police officer he was a "hitman" and gave "minute details" about Mr Maika's shooting.

The court heard Mazzilli allegedly referred to Mr Maika as someone who "snitched on things he shouldn't have snitched on".

Mr Maika was shot before the Golden Gun cocaine syndicate trial began but had already given his evidence in court in a committal hearing. He had refused offers of police protection despite concerns he could be targeted.

Homicide Squad commander Detective Superintendent Mick Willing said while police had a possible motive early, it was three years of "painstaking" investigations that led to the arrest.

"Every single day, people come forward and provide police with evidence. Every single day criminals give evidence against other criminals," Detective Superintendent Willing said.

"We have a range of mechanisms to protect those people who come forward. Unfortunately in this case Mr Maika declined all offers of assistance to him prior to his death."

The Golden Gun syndicate was one of the biggest drug groups broken up by Operation Schoale, a joint investigation by the NSW Police Force and the NSW Crime Commission.

Thirteen people were convicted for their roles in the syndicate, which imported and sold more than 300 kilograms of cocaine in 2005 and 2006.

The syndicate was paying $30,000 a kilogram for cocaine in Chicago and selling it for $190,000 in Sydney.

In the raids that broke it up in 2007, police netted almost $20 million in cash, property, motor vehicles, high-grade cocaine and 17 firearms, including a gold-plated .357 calibre pistol, which led to the name "Golden Gun" syndicate.

Sparos' partner in crime in the syndicate was Alen Moradian, known as "Fathead" to Sparos's  "Fatboy".

Moradian pleaded guilty in 2010 to importing cocaine and was jailed for a maximum of 16 years and nine months.

Moradian's wife, Natasha Youkhana, once urged him to behave more like New Jersey mafia boss Tony Soprano in the TV series The Sopranos.

"Why do you just sit there and show off – 'I am the man, I am the man.' Do you see Tony Soprano doing that?" she wrote in an email. "He doesn't care who people think is the boss, [money] is his number one priority. You, on the other hand, want the attention, you want the big head, you love it. People like that won't survive.''

Mr Maika had given evidence in a committal hearing relating to death threats against the chief Crown witness in the Golden Gun case, who was known as Mr T.

Mr T was a family friend who was also involved in the syndicate but became a Crown witness and entered the witness protection program.

Sources say Mr T's life remains at risk.

The seven major players in the Golden Gun syndicate are serving between five and 30 years in jail.