The sniper had taken up his position on the top floor of the eight storey tower block shortly before 9pm.

He tried to make himself as comfortable as possible while waiting patiently for his target to appear in view through the telescopic sight.

The concealed spot where he was positioned was normally used by residents to hang out their washing.

But today the concrete drying green had a far more sinister purpose.

Glasgow Times:

A few minutes later father-of-five Frank McPhie was lying dead outside the ground floor tenement flat where he lived in Guthrie Street, Maryhill, shot once through the head with pinpoint accuracy.

His terrified 11-year-old son had been playing nearby and saw his dad fall to the ground.

The killer walked off leaving behind the deadly weapon that had just delivered the fatal bullet - a Czech made ACZ Brno rifle.

The victim was one of the city's biggest underworld figures with an involvement in serious and organised crime going back to the 1970s.

Glasgow Times:

McPhie's death, shortly after 9pm on May 10, 2000, shocked the local community where he lived, but not one of the police officers tasked to investigate his murder.

Six weeks earlier Detective Sergeant Gerry Gallagher had stood in McPhie's flat which was only a short drive from Maryhill Police Office.

He'd been sent to deliver a threat to life warning also known as an Osman Warning.

They are issued to criminals where police have credible intelligence that violence is being planned against them.

Gerry says McPhie was unconcerned about the threat to his life and also made it clear his visitor was not welcome.

Glasgow Times:

He recalled:"I knew McPhie like most officers in the city by reputation and as a violent individual.

"But it was my first involvement with him personally.

"Though he was not tall he was powerfully and stockily built.

"During our short meeting he bristled with aggression but it was his eyes that told you everything "They held neither warmth nor humour.

"I told him that I was there to give him a warning that his life was in danger and he should take precautions regarding his movements.

"But he was not interested in hearing this.

"He said; 'you've given it, now goodbye.'"

Glasgow Times:

Gerry then became a key part of the murder investigation team and five months later was involved in identifying a prime suspect.

The tower block from where the gunman opened fire was in Carrbridge Drive directly across from the victim's home.

Gerry added:"The sniper just bided his time until McPhie came home.

"After he has fired the shot he just disappeared into thin air "There was no sign of a man running off or cars being driven away at high speed.

"It's possible he had a bolt hole in the same tower block where he could hide until things quietened down.

"He may even have just slipped sway and joined the crowds in the street.

"We later discovered that our main suspect was a local man who lived nearby so he would not have stood out or attracted any suspicion at the time."

Glasgow Times:

McPhie, a close associate of the late crime boss Arthur Thompson, had served time for armed robbery in 1978 and 1986 and received eight years in 1992 over a £200,000 drug seizure. He also had a keen interest in dog fighting.

In a chequered criminal career McPhie was also famously cleared on two separate murder charges.

One involved the murder of a fellow inmate William Toye at Perth Prison in 1996 for which he was cleared in 1997 However it was for the second murder in 1997 - three months after he came out of prison - that McPhie first came to public attention.

Glasgow Times:

The victim Christopher McGrory, 25, was not only a close friend but McPhie had been an usher at his wedding in Dublin two weeks earlier.

McGrory was found strangled in the back of his own van at the side of Dougalston Golf Club, at Milngavie.

Glasgow Times:

Glasgow Times:

Frank was arrested along with 29 year old Colin McKay - Christopher McGrory's best man.

Both were cleared at the High Court in Glasgow in 1998 and cheered by a jubilant crowd of 50 as they left the building.

It was thought that McGrory, who owned three horses, had been murdered over a drugs deal gone wrong.

The second acquittal cemented McPhie's reputation as a major player.

He now had no need to fear or be wary of offending other criminals - or so he thought.

McPhie was shot after parking his van on nearby Kelvindale Road to walk the 20 yards to his flat.

Was this assassination revenge for the murder of Chris McGrory three years earlier or did the answer lie closer to home?

McPhie had also been involved in a road rage incident on Balmore Road, in nearby Lambill, with a young member of the notorious Daniels crime family.

He is said to have arranged to have him ambushed and stabbed outside a local Chinese takeaway.

McPhie was also said to have pulled pull up his mask to let his victim know who was responsible.

He even turned up at a Daniel's scrap yard in Maryhill, to show that he did not fear any reprisals.

It was this series of events relayed to police that had led to Gerry issuing the threat to life weeks earlier.

Although no evidence has ever been found to link the daniels family to the murder.

READ MORE: Glasgow crime stories: Philip Wong

Gerry said:"I wondered whether his two murder acquittals had given McPhie a mistaken sense of his power or invincibility.

"My father once told me that no matter how cute, hard or dirty a football player you thought you were, there was always someone cuter, harder and dirtier."

Police hit a wall of silence during their investigation into McPhie's murder.

They had little or no evidence and there was also a lack of witnesses.

Given the various factions that were known to be involved it was not surprising.

DNA was later discovered on the weapon but it belonged to one of the police forensic scientists.

A photofit of a possible suspect seen in the area at the time of the murder also brought a poor response.

Five months into the inquiry Gerry and a colleague working the case got the breakthrough they were looking for.

They discovered that the murder weapon had previously been used as target practice on a telegraph pole in a farmer's field near Kilmarnock in Ayrshire.

READ MORE: Glasgow Crime Stories: Barlinnie

A witness gave them a name and a 37-year-old man from Maryhill was arrested for the murder. He also happened to be a key associate of the Daniel's family – remove.

The man appeared at Glasgow Sheriff Court on October 6, 2000, but the charges were later dropped through lack of evidence and the 37-year-old was never prosecuted.

Gerry added:"It was slog for the police because of who the victim was and the family said to be behind the murder.

"There were not many tears being shed for Frank McPhie.

"In these types of inquiry the general public understandably do not want to get involved.

"The problem was that we did not have any eye witnesses.

"All we had was the evidence from the farm but that was not enough to go to trial."

In 2014 leading criminologist Prof David Wilson theorised that the murder had been carried out by a master hitman.

The Scotsman examined 27 murders carried out by 35 hired assassins included the unsolved murder of Frank McPhie.

Wilson, who lectures in criminology at Birmingham City University, said at the time: "Hitmen are familiar figures in films and video games, carrying out hits in underworld bars or from the roof tops with expensive sniper rifles.

"With the exception of McPhie, the reality could not be more different."

READ MORE: Glasgow Crime Stories: The murder of Alex Blue in the West End 18 years on

Wilson identified four types of British hitmen - the novice, the dilettante, the journeyman and the master.

He added:"It's quite clear that McPhie's killing was carried out by a master hitman.

"Like most master hitmen, McPhee's murderer was never brought to justice."

More than 20 years later his assassination is now a cold case investigation subject to occasional reviews by Police Scotland.

Gerry added:"Whoever did it knew what they were doing. It was well planned and executed.

"People may not have mourned Frank McPhie's passing but every murder victim deserves justice regardless of reputation."