Kemel Barakat's new address was supposed to be secret, yet his killers knew where he was.

His apartment block was supposed to be secure, yet they were able to creep into the building and through the front door without needing to force their way in.

Once inside the bedroom of Barakat's apartment in Sydney's inner west, they unloaded more than a dozen bullets at close range, killing the Hells Angel bikie as he slept in his boxer shorts.

Even in the bloody world of gangland executions, this killing was brutal.

Unlike the potentially linked assassinations before it, this hit was not carried out in the public arena, on a street, outside a house or in a cafe. It was well-planned. The killers were well-informed. Investigators and some in Barakat's inner circle suspect it required the help of someone close to him.

The cold-bloodedness of the killing has sent some of Sydney's most powerful underworld players into hiding

Fairfax Media understands Barakat's close associates, including Ahmad "Rock" Ahmad, brother of slain crime figure Wally Ahmad, have fled their stomping ground in the south-west suburbs. With their families in tow, the associates, notorious figures in their own right, have taken refuge in apartments in Sydney's east in the past week, anxious they will be targeted next.

"Now these blokes and their families have to be bunkered down and living in hotel rooms for fear someone is going to pop them," one source said.

"They are scared," a police officer put it simply.

Some of the figures now constantly looking over their shoulders braved the potential threats to attend Barakat's rain-drenched funeral in Marrickville on Thursday. Others skipped it, acknowledging tensions were high.

As is the case after any gangland murder, police are wary of imminent and violent retaliation. They are also concerned that the brutality of Barakat's death is a sign of worse things to come.

Barakat, also known as "Blackie", was murdered in his Mortlake apartment after he emerged as a suspect in the shooting of crime figure Hamad Assaad. Like Barakat, Assaad was a suspect in the shooting of notorious standover man Walid "Wally" Ahmad last April.

The recent tit-for-tat shootings appear to have roots in a fierce battle between some of the south-west's most feared families and their associates.

Barakat, a 29-year-old with a family base in Marrickville, found himself intertwined with the Ahmad network only in the past couple of years. He had a long affiliation with the Hells Angels, as his tattoos showed, but his loyalty to his mate Rock, more than a decade his senior, became of particular interest to police.

Their partnership came at a time when the Ahmad family had been dealt a succession of heavy blows and the pressure to save face was on.

It was April 2016 and Rock's brother Wally, a charismatic, larger-than-life figure and established career criminal, had just been killed. The 40-year-old was sitting at Havana Cafe in Bankstown Central after a gym session when a man ran towards the heavy set figure and fired multiple rounds. Wally bled out on the tiles of the cafe as his brothers turned up demanding to see their dying sibling.

It was a significant blow to the criminal network. Wally was a widely recognised figure in the area. He demanded rent from dealers plying the Bankstown/Punchbowl drug trade, mediated everything from conflicts over drug rip-offs to business disputes, and stood over honest business people for his own benefit.

After completing a six-year jail term for shooting Mayez Danny at Greenacre in 2002, sources say Wally was trying to re-establish himself in the south-west criminal world. While Wally was predominantly the face of the Ahmad family, Rock was the less exposed yet equally influential sibling in the background.

A few weeks before Wally was killed, his younger and more volatile brother Mahmoud "Brownie" Ahmad travelled to Lebanon. His journey out of the country came after he was allegedly involved in a deadly gunfight between the Ahmad and Elmir families outside Wally's smash repairs shop in Condell Park.

Over the course of the lengthy confrontation, which spilled out onto Ilma Street, a gun was pulled and 32-year-old Safwan Charbaji - related to the Elmir family by marriage - was shot dead.

A few days later, Brownie left. He was effectively helpless as, from Lebanon, he watched his brother Wally's murder unfold.

Police speculate that the absence of two brothers and the dwindling strength of the family may have led the Ahmads to soften their historical disdain for outlaw motorcycle clubs.

"After the Wally stuff they started to become quite vulnerable as they are not used to being on that side of the gun," one source said.

The Hells Angels wanted to set up a chapter in the Punchbowl area but they needed permission to do it. Providing the green light for the Hells Angels in Punchbowl could have given the club access to a drug run and potentially bolstered the strength and support base of the Ahmads and associates.

According to the club's website, it set up the chapter in 2016. However, police say there has been recent tension and confusion over whether the Ahmads ever gave their permission for the Hells Angels to gain a foothold on their turf or if that agreement folded.

It is an example of how loyalties, governed by family or ethnic lines, chop and change, particularly in the Middle Eastern organised crime sphere.

Former police assistant commissioner Ken McKay, who helped establish the Middle Eastern Organised Crime Squad, said allegiances changed depending on where a personal benefit could be found.

"And some of the people that were on the right yesterday are now on the left," he said.

There was no doubt the absence of some brothers would impact the Ahmad family, McKay said, but they could draw strength from elsewhere.

Parallels have been drawn between the current conflict and the violent feuding between the Lebanese Darwiche and Razzak families in the early 2000s.

Asked what it took to end tit-for-tat shootings such as these, McKay said: "It comes to a stop when they all get locked up or they are all dead.

"It doesn't end pleasantly."

After Wally's death last April, police were braced for what seemed to be inevitable retribution. But none came. While the list of people who wanted Wally out of their lives was long, there were no solid suspects.

It was at this point that crime figure Hamad Assaad got cocky. He had kept quiet about Wally's death but, comfortable with the belief police had nothing, he started talking.

Underworld sources say the 29-year-old, investigated for shootings, drug rips and extortions, began mouthing off about how he killed the notorious crime figure.

He was socialising with Hells Angels bikies at the time, including rumoured national president Dallas Fitzgerald. He had fallen out with mafia figure Pasquale Barbaro, who was shot dead a few weeks later.

In October 2016, as he prepared to take a relative to school, Assaad was shot dead in a well-planned assassination involving four people. His execution was captured on his own CCTV system.

It wasn't long before Barakat emerged on the radar as a suspect in the shooting. While a friend close to his family conceded he was in the frame, they say if anything, it was more likely he was a driver in one of the getaway cars.

Investigators say Blackie wasn't known for putting on a show but from that point he was thrust into the police spotlight.

The Middle Eastern Organised Crime Squad used powers associated with firearm prohibition orders to search his house regularly and unapologetically without a warrant. He had been in his Mortlake unit for about a month when he was killed but had already started making plans to move.

On the night of March 9, police visited him again, this time for a bail compliance check. Barakat was due to face trial for drug supply in May.

Hours later, at 2.30am, intruders entered the unit, where a woman - now a murder witness - was also staying. The woman, a hairdresser from the south-west, emerged from the apartment that night unscathed while Barakat succumbed to his gunshot wounds.