But the man many would love to see in the dock answering questions over four murders, Robert "Bluey Bob" Mather, will not be there for a perfectly good reason. He is dead and, unlike the murder victims, he died in 2014 surrounded by family rather than at the hands of a paid stranger.

Mather was well liked in underworld circles and had the gift of the gab, that is unless police were questioning him. Then he would turn from loud and funny to silent mummy.

In many cases, he was more of a facilitator than hands-on, but police are convinced he knew much about a series of unsolved murders, along with several lucrative armed robberies committed over nearly 20 years. His role in at least one of the killings will shortly be examined at the much-delayed inquest into the murder of bouncer George Germanos, ambushed in an Armadale park 15 years ago.

The long-held theory is Germanos was set up because he bashed Mather's son Ray outside a St Kilda nightclub on October 21, 2000.

Five months and one day later, the bouncer was dead, shot once in the chest and four times in the head in a classic underworld ambush.

Police have linked the Underbelly murders of Germanos and Dimitrios Belias​ (in 1999) with the seemingly motiveless killing of young mother Maryanna Lanciana 15 years earlier.

Mather was also linked to the killing of Shane Chartres-Abbott, the so-called vampire gigolo prostitute (try putting that on a business card) shot dead in 2003.

First to Big George. The former power lifter knew he was in danger when he discovered the snoozer he put to sleep outside the nightclub was Mather's son.

Just two weeks before he was killed, he tried to borrow $5000 from a relative to buy a handgun. "He said: 'I'm in trouble; there's a hit on me. I've bashed a kid. I didn't know who he was'," the relative said. (There is no suggestion Ray Mather was aware of any plot against Germanos).

"He wasn't a career criminal. He was a quiet man who still lived at home. But from working security at clubs, he knew a lot of wrong people."

And it was some of those wrong people who set him up.

"We have been waiting 15 years for answers to what happened. We desperately want the inquest to go ahead without any further delays," the relative said.

On March 22, Germanos went to Armadale's Inverness Park for a late-night meeting. The open street directory later found on the passenger seat of his 1966 Valiant would suggest he did not know the area and the location was selected by his killer.

It was the perfect place for a murder, as it was covered with trees, intersected five streets and offered easy getaways.

Between 10.30pm and 11pm, he parked about 50 metres from one of the park's entrances and walked in, leaving his cigarettes and lighter in the car. (He left his mobile phone and wallet at home.)

If his plan was to slip into the park unnoticed, it failed. The killer beat him there and almost certainly hid under a bush near the entrance. Germanos walked in five metres, then turned back, possibly after the killer called his name.

The last thing he saw was the muzzle flash as he was shot in his barrel chest. Then the killer shot him four times in the head from point-blank range.

It is easy to speculate, but the planning of the ambush and the ruthless execution suggests the gunman was no novice.

Police suspect the hitman was a man close to Mather, who had freelanced for him before.

Which brings us to Belias, a con artist who always seemed to have several balls in the air. But when he tried to rip off Mather, one of the balls turned into a hand grenade.

Belias was an underworld debt collector heavily in debt. He burned in a loan scam the type of people who don't need to call consumer affairs to get their money back.

On September 9, 1999 (9/9/99 – lucky for some, but not for others) Belias had several meetings, with the last planned for 7pm in St Kilda Road.

He drove into the city and parked outside the Regency Hotel and at 5.47pm Bluey Bob hopped into his car for a chat.

He was the last known associate to see him alive and, as usual, Bluey refused to make a statement to police.

Belias was lured to a meeting in an underground car park in St Kilda Road and just before 7pm was shot in the back of the head.

A muzzle imprint on the skin indicated the barrel was pressed against his skull.

So, how could these underworld killings be connected to the murder of a young mum in Werribee?

First, we need to look at Mather's wider social circle, which included a group of loud detectives and a gang of quiet crooks. The crooks, we now know, formed an armed robbery gang right out of a George Clooney Ocean's 11 movie.

Fit and well trained, they would meet secretly in public parks and carry out meticulously planned armed robberies on the Olympic schedule of every four years.

Each job was different with one common element: they always had an inside man, once leaving a sleeper in place for years until they were ready to move.

Over 20 years, the gang invested the stolen millions in property and businesses, avoiding indulgent purchases that could attract the interest of police and tax officers.

After each robbery, they would disperse to live seemingly law-abiding lives, running businesses and bringing up children. Some worked as part-time actors, scoring roles in a local cop drama that featured a major armed robbery. Talk about method actors.

But occasionally the cloak of invisibility would lift, such as when they turned up at certain underworld funerals to be given prominent positions in the mourning party.

Which brings us to the murder of Maryanna Lanciana​, 25, in Werribee in July 1984.

She, like Belias, was shot in the back of the head at point-blank range. The gunman snuck into the Kiely Avenue house and shot her while she slept in her bed with her 22-month-old son asleep in a nearby cot.

But why? The suggestion is she fell on some information about the armed robbery gang and was callously dealt with like an errant thread in a favourite suit.

In one way, it worked, as many on the periphery were frightened into silence – at least until recently.

Fear is a powerful deterrent, but greed, coupled with the desire to do a deal when police come knocking, is the equally powerful antidote.

In 2014, when announcing an unprecedented collective $3 million reward for information about the killings, the then head of the homicide squad, Detective Inspector John Potter, said: "We have information the three murders are connected and there will be people in the community who have associated with a particularly criminal group with information that can assist us."

What we do know is after years of near  monastic silence underworld birds are chirping and police believe one gunman may be responsible for pulling the trigger in all three cases.

How much of this will be revealed at the Germanos inquest is anyone's guess, but when the matter came up for mention a couple of weeks ago before the State Coroner, Judge Sara Hinchey showed distinct signs of growing impatient at a series of delays.

Intriguingly, the file was coupled with the murder of Shane Chartres-Abbott, who was gunned down on June 4, 2003, in the driveway of his Reservoir home.

The Chartres-Abbott murder opened a drum of spitting pythons rather than the usual can of worms.

In 2007, a notorious underworld killer turned informer volunteered to detectives he was the trigger man in the Reservoir hit.

This was intriguing because in other cases when he confessed it was always out of self-interest, minimising his involvement and maximising his sentence discount.

This time, he admitted he was the shooter when he was not even the suspect.

He was convicted of the killing and his statements resulted in three men being charged – and acquitted.

Although he was never charged, it was claimed Mather was the facilitator.

There were allegations that corrupt police close to Mather were involved – claims the now former police have always denied.

For the first time, police are using a retired investigator to prepare the (Germanos) brief for the coroner. The choice of investigator, respected former detective inspector Steve Waddell, is no fluke. For he was in charge of Taskforce Briars, the protracted investigation into the Chartres-Abbott killing.

Some years back, Waddell publicly identified a suspect who sounded suspiciously like Bluey Bob. "He has flown under the radar all his life. He's in his 60s and has never had a legitimate business."

Mather is now beyond reach, but the trigger man or men are not. And revenge, justice and three-day-old pizza are often best served cold.