Sparos needed a gun, it is alleged, and the clock was ticking with his May court date looming.

He asked his mate what he had organised.

"I got a 22 for $5000," the associate offered.

"What's that going to do?" Sparos retorted. "That's not going to be big enough … I need something with more calibre."

In the end it was a .45 calibre pistol that shot dead Sparos' alleged target – a witness he was "determined to silence" for talking to police about a cocaine importation and supply.

A month before Sparos was due to face trial for drug allegations, prosecution witness Gemahl Maika was shot five times outside his south-western Sydney home.

The unusual case is one in only a handful of cases around Australia that centres on the alleged killing of a Crown witness.

Having given three statements to police and evidence in court about his own involvement and knowledge of the drug supply, Maika escaped charges.

While Maika was free to return to the Glen Alpine home he shared with his family each day, Sparos was occupying a cell in wing 13 of the Long Bay Correctional Centre.

It is from this prison that police allege Sparos instigated a plan to have Maika murdered as "retribution".

It is alleged Sparos, 35, enlisted "killer for hire" Maximillian Mazzilli to carry out the hit, while also using his brother-in-law Anthony Saliba as a "conduit" in the planning.

The NSW Supreme Court, where all three are on trial after pleading not guilty to murder, has heard startling details of the alleged murder plot this week.

Sparos' wife, Christine Saliba, is also on trial, having pleaded not guilty to being an accessory before the fact to murder.

The 36-year-old is accused of helping her incarcerated husband in preparing for the alleged murder.

Maika arrived home from his thrice-weekly Campbelltown TAFE course on April 6, 2011, about 9.40pm and parked his ute in the garage.

It alleged Mazzilli, wanting to "surprise him" and armed with a .45 calibre pistol, walked up behind Maika as he got out of his car.

Mazzilli later allegedly recounted to an undercover police officer how he called Maika's name before "pow, pow, pow".

The Crown says Maika fled out of his garage and towards his neighbour's property as six shots were fired.

He made it to the front yard before he collapsed near a boat parked on the grass.

Five bullets hit Maika's body, four around the chest area and one in the head.

His 22-year-old stepson, having heard the commotion from his bedroom, found Maika on his elbows and knees, covered in blood.

An emotional Raniera Kidwell, now 27, told the court this week he heard his stepfather say "who the f--k are you?" or something similar while in the garage before the gunshots rang out.

It would take three years and an undercover police operation before Maika's family learned who the Crown alleged was responsible for gunning down the 38-year-old.

In 2014 Mazzilli was at a Tweed Heads hotel on the NSW North Coast and allegedly told an undercover police officer about his last target.

"I have my credentials …" he said, according to Crown prosecutor Craig Patrick.

"The last one was a message … left for everyone to see."

Mazzilli, 35, allegedly claimed he knew Maika's wife was inside the home that night and was even an arm's length away from his stepson when he came outside to switch the power back on after Mazzilli flicked it off.

"He was lucky I'm telling you …" Mazzilli is accused of saying during the 2014 conversation.

He asked the officer if his phone was "clean" before punching "Glen Alpine shooting" into Google.

"Have a squiz at that," Mazzilli suggested.

The alleged gunmen made reference to using a "45", a detail police say they kept out of the public eye after the shooting.

The undercover police operation saw Mazzilli allegedly enter into a contract to kill someone, the court heard.

However, when he travelled to Sydney in July 2014 to carry out the hit on this factitious person, he was arrested.

Mazilli's defence claimed this week he picked up the details of the Glen Alpine shooting in media reports and through jail talk and wasn't responsible for pulling the trigger.

His barrister Linda McSpedden submitted Mazzilli set about to "ruse" the undercover officer where he would take money to carry out a shooting but not actually return the service.

The Crown says Mazzilli also told the officer his last target had "snitched on things he shouldn't have snitched on".

Those things were allegedly the details of a cocaine supply and importation operation targeted by the NSW Crime Commission.

At the head of the investigation – named Operation Schoale – was Mark Standen.

Standen was later sentenced to 16 years jail for his own drug importation and Sparos held onto hope he would be granted a stay on his case because of Standen's conviction.

Sparos' defence barrister Con Heliotis, QC, submitted this hope, coupled with an offer to plead guilty to drug supply of a lesser amount, contributed to why he had little reason to punish Maika.

Maika's statements only made up a very small part of the case against Sparos and his co-accused in the drug trial, Mr Heliotis told the jury.

The Crown alleged as Sparos formulated his plan to seek retribution, he managed to get Maika's home address through a fellow inmate in late 2010.

He also shared Long Bay jail's wing 13 with Mazzilli, who was due to be released but was allegedly part of Sparos' plan.

"It was a plan where Mazzilli would kill Mr Maika at the request of Mr Sparos for the payment of money," Mr Patrick told the trial.

Mazzilli later told the undercover officer he was paid $200,000 to carry out the hit.

In an attempt to keep the plan discreet, another inmate was allegedly brought into the mix as the point of contact for Mazzilli.

That inmate would then deal with Sparos' brother-in-law, Anthony Saliba, who regularly visited Long Bay with Sparos' wife, Christine.

In late 2010, their conversations were peppered with "coded language", the court heard, in a prison environment where some communication is legally recorded.

While his relatives allegedly helped Sparos in his aim to kill a police witness, the 35-year-old was the accused mastermind.

"It is alleged in this trial that Sparos instigated the murder," Mr Patrick told the jury.

"He was determined to silence the witness in the case against him."

The trial before Justice Michael Adams continues.