It was from this rosy residence in Sydney's inner-city suburb of Alexandria that the Italian man was heard sonorously singing on Easter Saturday morning of April 7, 2007. The neighbours were used to his gusty operatic renditions. But then there was a sudden silence. Soon after, the morning was shattered by a terrible noise coming from the house, a wailing and screaming that brought the street to a startled stop. Mario Guzzetti, 72, had been singing Andrea Bocelli's Con Te Partirò (Time to Say Goodbye) when he suddenly died.

At 9am, the phone rang. It was Giuseppa di Francesco, a friend who was ringing about some Easter biscuits she had made. All she could hear down the phone was crying, there were no words. She rang her husband, Giovanni, who arrived at the house a few minutes later. He phoned his wife saying, "Mario is dead, he has had a heart attack," before phoning the police.

Di Francesco was outside in the street having a cigarette when the ambulance officers arrived at 9.20am. Guzzetti's head was being cradled on a pillow in the lap of his partner, Philip Leung, then 47, who was sitting on the terrace's polished wooden floor. Guzzetti's skin, noted ambulance officer Lawrence Agars, was "pale blue". Leung was, he later told the court, "hysterical. He was rocking the patient's head from side to side. He was crying very, very loudly. He was just screaming, 'Wake up, Mario, wake up, come back, don't leave me!' "

Even though he had incoherently called the emergency services at 9.12am, saying, "I had a fight with my friend and my friend is dead" and hung up weeping, Leung now wouldn't let the officers near his beloved. "When I moved closer to the patient," said Agars, "the Asian man would swing his arms at us." When they tried to talk to Leung, "he just looked at us and cried". He was making such a racket that the officers had to go outside to radio the police to come and manage him so they could assess Guzzetti.

The medicos finally prised Leung from his partner. "He began rolling around on the floor from side to side. He was still crying hysterically and very, very loud. He intermittently tried to get up and crawl closer to the patient," said Agars.

Leung was still writhing on the ground when the police arrived at 9.45am. While they restrained him on a chair, the paramedics ascertained that Guzzetti was a "code four" - deceased. Agars noticed that he had a "cross-shaped laceration on his right jaw", and there was a "small metal pot with a spout near his leg". There was blood on the stair rail, the wall, the door jamb and Leung's shirt. Leung was beyond reach. "He appeared," said Senior Constable Graig MacInnes, "not to comprehend anything that was said to him."

As Guzzetti's head was covered with a blanket, Leung became so distressed that the police handcuffed him so he could not harm himself or anyone else. "They are not helping him," he shrieked, trying to bolt from the paddy wagon to comfort Guzzetti. His shock was so great that he couldn't accept Guzzetti had gone, telling his friend Ray Carter at the police station, "Mario is not dead. He is only in hospital. I didn't kill or murder him." He also told Carter in front of another sergeant, "We have breakfast. Mario argued with me, he criticised me a lot. Then my head started spinning and I don't know what happened."

Inspector Stephen McCormack would tell the court that at Redfern police station, Leung was "acting differently to what I would expect. He was very nervous, evasive. It wasn't clicking right in my mind." Says Ray Carter, "He had learned in China that you say nothing to the authorities."

Leung was never offered the medical assistance or the sympathy the abruptly bereaved are entitled to expect. The fastidious pink house he shared with Guzzetti became a crime scene. And Leung would go on to become, perhaps, the unluckiest man in NSW.

Leung now knows how thin the membrane is that holds us all together. What infinitesimal degrees of luck and accident separate a routine morning in an ordinary suburb from one that starts a descent into the nine circles of hell.

The argument that morning was over carrot juice. It was hardly the kind of domestic spat that would drive a man to murder. But by the end of that morning, Leung would be in prison, charged with the murder of a man he had loved very much. And this would be the beginning of a terrifying, six-year rollercoaster ride through the NSW courts.

According to Leung's testimony, Guzzetti was sitting in the living room when Leung told him the juice was ready. But Guzzetti decided he didn't want it. Leung emptied the juicer, then Guzzetti changed his mind and wanted a juice after all. Leung started peeling carrots again, only for Guzzetti to change his mind yet again. Exasperated, Leung says he shouted at him, "flicked" the juicer at the wall and went out into the garden to calm down. Unperturbed, Guzzetti went upstairs in his tracksuit pants and Italian leather slippers, warbling away.

Suddenly, hearing a loud thump, Leung says he found his lover lying face down at the bottom of the stairs. He turned him over and tried to resuscitate him.

Those who know Leung well say he is excitable, emotional: that he can erupt into a tizz, but that it is harmless. "It would be forgotten in five minutes", says Peter (not his real name), who lived with him for eight years in a mostly platonic relationship before Leung moved in with Guzzetti in 2003. "He would scream and yell at you, but I swear on a stack of Bibles, he was not a hitter. I had many rows with him, but never once did he throw anything or attempt to hit me. He would walk away, slam the door and it would be a day or two before you saw him, then it would be as if nothing had happened. That is how he handled it. He would go and sit in the park or a gay sauna, or spend all day in an art gallery."

Guzzetti used to joke about Leung's infamous bluntness, says Peter. "He would say, 'It was a good week, this week - Philip was only rude to one person.' He was very happy, very sociable, but very rude to people. Philip is an artist, he is very talented and he has got that temperament, very rude, very arrogant. That is what got him into all this trouble. He was very short with people. If he liked you, he would do anything for you, but if I had friends over for dinner he didn't like, he would go out or shut himself in the computer room and ignore them."

Ron Johnson, 66, is a practice manager for a doctor in Blacktown. He met Leung through mutual friends at a dinner more than 20 years ago and is a staunch ally to his old friend. "He can be embarrassing at times because he warms very readily to someone he likes - maybe the shop owner serving him, or even another customer - or he can get into conflict with those people. It would not be unusual for Philip to burst into opera in public. He becomes passionate in conversations about subjects like politics, cultural differences and people he might consider rough or stupid. He can be a bit loud because he is so outgoing."

As murder weapons go, it would have to be one of the more unlikely to have come before the Supreme Court of NSW. The bowl, part of a juicer, weighs about a kilogram. Not exactly lethal. Yet the Crown insisted that Leung had used it three times to strike Guzzetti, using enough force to make him fall down the stairs to his death.

"Mario would not have passively allowed himself to be repetitively hit," says Ron Johnson. "He was bigger than Philip and very fit and strong. There were no marks on Philip to show that he had been involved in a physical fight."

Says Peter: "They were about the same height, but Mario was 15 kilos heavier."

There were scratches or "tear" marks on Guzzetti's skin, but no DNA under Leung's fingernails. The house had been tidy, with no signs of a physical struggle. Fragile pieces of antique furniture and sculpture near where Guzzetti was found were undamaged.

Does a man in fear of his life walk around singing? And since the neighbours heard everything else, surely they would have heard a fatal fight?

An autopsy found that Guzzetti had received a blunt-force injury to his head and neck, which could have been caused by a blow or by hitting it on a wall or staircase. He had hypertension, scarring of the liver, fluid on his lungs, an enlarged heart and three partly blocked arteries. There were bruises and torn skin in his mouth, on his neck and chest, on his head, on his arms, knuckles, back and hips, which could have been from a fall down a narrow, winding 1880s staircase, or caused by an attack. Marks on his neck could have come from an attempt at strangulation, a clumsy attempt at resuscitation by Leung, or by the ambulance officers doing their job. "I identified the body," says Peter, Leung's ex-partner. "There were no visible marks on his face."

Guzzetti also had the DNA of an unknown person under his fingernails. This has prompted his friends to wonder if someone else was in the house, although as far as Good Weekend understands, the police have never pursued this scenario.

The Crown's case was much more clear-cut. It argued that Leung struck Guzzetti on the head with the juicer, causing him to fall down the stairs, hitting his head on the way, which led to his death.

Wan Por Leung was born in January 1960 in China's Guangdong province, 24 kilometres from the border of Hong Kong. (He would later change his name by deed poll.) "He grew up during the Cultural Revolution, and from the age of three they would pick him up in a truck and go to work in the rice paddies," says Peter. "Had he had a decent education, he would have had several degrees. He is a very intelligent person lacking an education."

His father fled to Hong Kong when Leung was very small to get a job to send money to support him and his four sisters. Leung's mother, exhausted from working in rice paddies to augment the family's meagre income, told him there was nothing to return to.

When he was 14, Leung's mother died of a stroke in the car park of a hospital she had rushed to, feeling decidedly unwell.

Soon after her death, Leung made the first of five crossings of the Shenzhen River into Hong Kong to try to find his father. Each time, he spent considerable time in the water to escape the watching border guards - on one of these attempts he was in the river for 15 hours. "When he got there he had nowhere to go, so the British kept throwing him in the stockades and sending him back," says Peter. Sometimes it would be a couple of months, sometimes a couple of weeks in prisons that were so crowded he had to sleep standing up.

On his final attempt, he met a farmer who knew his father. The farmer hid him from the Hong Kong border police in his truck and took him to his long-lost parent. Reunited but strangers, Leung and his father had almost nothing in common. His father had a tyre shop and wanted him to fit and change tyres. Leung tried but only lasted two weeks before he ran away after his father beat him up.

He wanted to become a ballet dancer but injured his foot, so found an apprenticeship in ivory carving while studying English at night. In 1984, the company he worked for sent him to New Zealand, where he worked carving jade for four years. He made his way to Australia in 1988 and later took out citizenship, though he never fully mastered the English language.

In Sydney, Leung went to Randwick TAFE and got a certificate in Jewellery Design and Manufacture. "I went to his graduation day, " recalls his friend Ron Johnson, "and saw his display cases of polished opals."

Peter remembers a wealthy man asking Leung to put a zircon stone into a 24-carat gold ring. "He wouldn't do it, he told him to bugger off. He said, 'Why do you want to put a fake diamond in 24-carat gold?'"

He describes Leung as an aesthete. "He never made a lot of money, he didn't want money - he was the true artistic type. He was more interested in creating art or jewellery, or ceramics and pottery, or sculpture. I never saw him buy clothes, he used to make his own - brocade jackets, his own shirts - he was multi-talented. He didn't drink alcohol; he would drink only water or green tea. He was wafer-thin, he never used spices in cooking. He lived on fruit. He would rather go hungry than eat a hamburger. He was scrupulously clean. He was almost a monk."

In 2001, Leung, then aged 41, met Mario Guzzetti, 66, at an opera function. Guzzetti was a retired printer who had worked for the Italian-Australian newspaper La Fiamma. They moved in together in 2003, initially to Guzzetti's house in Homebush, before buying the house together in Alexandria.

Everyone loved Mario. "Mario was absolutely beautiful," says Peter. "Very cultured, well-educated. He was a lovely man. He was very placid. They were both opera buffs - the ballet, the arts, that was their bond."

Indeed, Guzzetti was from that most cultured city of Verona, in Italy's north. He went to the library to read daily. With season tickets, they would go to the opera every Tuesday night and sit in the same seats; row three, seats 21 and 22. Leung was learning Italian. They were planning a trip to China with their friend, Ray Carter.

Says Johnson, "I think he did fall in love with Mario's background, the fact that he was Italian and they have statues of David and things like this. The Italian opera, the style, the old world ... That he was the old, original Italian homosexual."

In June 2005, Leung was attacked by a man whose advances he had brusquely rejected in a club in Darlinghurst's Oxford Street. After telling the guy to "f... off", he was stabbed in the eye with a ballpoint pen so viciously that it had to be surgically removed; he now has a glass eye. Leung never fully recovered from the physical trauma or returned to paid work, living on a disability pension. "Mario nursed him," says Johnson. "He used to massage him." Leung was unable to identify the perpetrator.

After Guzzetti's death, Leung spent five months in Silverwater Correctional Complex, before being granted bail by Justice Robert Hulme at his committal hearing.

Justice Hulme said he had only a "small window" in which to grant bail, but he believed there were insufficient grounds for murder charges. When he was freed on bail, Leung could not live in his home because his neighbour, Fiona Cunney, had been a witness against him. Peter's daughter invited him to live with her.

Says Johnson, "I remember we took him back to the house and he sobbed and sobbed on the doorstep. We couldn't get him past the front door and into the house where Mario had died. It seemed like all his grief had come all at once."

While Leung was in prison, Guzzetti was cremated and his ashes taken back to Verona in Italy, a place he had left in 1958 and, says Johnson, he "never wanted to go again. He always wanted to be buried here. This was his home." None of his and Leung's friends was present. "Mario's funeral arrangements were kept from us, despite my request to the police for information," says Johnson.

Leung would later tell The Sun-Herald, "Not only did I lose the man I love. I was accused of killing him and locked up in jail. Nobody cared that I missed Mario's funeral, or that I had as many questions as anyone."

Before his trial started in April 2009, Leung was offered a deal of manslaughter in exchange for a guilty plea. He refused, declaring, "I didn't do it." Facing 28 years in prison, he was gambling his life. "He believed in the system to prove his innocence," Peter says, "and he never wavered."

"I had a fight with my friend and now he is dead." This small sentence, uttered in shock and grief, has been interpreted by the prosecution as an admission of murder. But could it also be the agonising guilt felt by a man whose last exchange with his partner had been one of anger?

Johnson says because of language difficulties, Leung’s "sentences can run together and come out wrong and be misunderstood. What he meant was, 'The last thing I remember is that we had an argument and now he is gone and I can't undo it.' "

In Alexandria, their neighbour Fiona Cunney had a sleepless baby and a thin common wall. In addition to the opera obsession, Leung and Guzzetti were renovating. Angry words were frequently exchanged, agreements to stop the noise on weekends were broken.

Says Ron Johnson, "You mix an Italian guy with a Chinese guy and see how much noise they can make. They had a Bose sound system. They deliberately did things to annoy her. Mario apparently disliked her to such an extent that he would walk out into the back yard naked, point his bum in her direction and fart."

In the days before Guzzetti's death, Leung had really let Cunney have it, to the point that Guzzetti had felt compelled to apologise. She would tell the court that the day before Guzzetti died, she had heard Leung screaming menacingly at either Guzzetti or a tradesman over a bag of tiling cement that had been left by the door. If the screaming was directed at Guzzetti, it couldn't have been that severe, the defence pointed out, since the couple had had consensual sex before breakfast the next morning.

Cunney told the court she heard what "sounded like a shelf falling with pots and pans on it and lids rolling on the floor, lids or a lid, one lid or several" at 8.15am, meaning there was a suspicious gap of 57 minutes between the fall and the phoning of emergency services. Leung vehemently denies this time frame. Cunney also said that Leung's wailing sounded "like a temper tantrum". She admitted that she had often fallen down her own identically treacherous, narrow staircase.

Giovanni di Francesco, who owned a gelato bar in Newtown, was an old acquaintance of both men (his wife Giuseppa swapped Italian recipes with Guzzetti and Leung drove her to the Flemington Markets to buy fruit and vegetables). Di Francesco testified that Guzzetti had told him a month before he died that he was thinking of ending his relationship with Leung and selling the house because he, Leung, was becoming too aggressive. But Peter doubts whether Guzzetti really did want to end his relationship with Leung.

It is not known why di Francesco turned against Leung. Three days after his arrest, Leung asked Peter to visit di Francesco and tell him he was all right. "When I entered Giovanni's shop, he was clearly uncomfortable when he saw me; if he could have avoided me he would have," says Peter. "He said, 'I don't care; he is a murderer.'

He then went ranting on about Philip being crazy. I was gobsmacked."

So how, then, did Mario Guzzetti actually die? We still don't know for sure. The medical evidence, Justice Stephen Rothman noted, was "ambivalent at best". Guzzetti could have received these injuries from a "complex" fall down the stairs, scraping and bruising his skin on the narrow steps and hitting his head on the balustrade with its protruding bollards, though this was, according to forensic pathologist Dr Paul Botterill, at most "a theoretical possibility". Or he could have been attacked. Leung's friends believe it was as simple as a heart attack.

On May 4, 2009, Justice Stephen Rothman directed the jury to return a verdict of not guilty of either murder or manslaughter. "Since the act of causing death is not proved beyond reasonable doubt, it is mere conjecture to suggest that the accused committed an unlawful and dangerous act."

Leung said he had felt Guzzetti with him "every step of the way". The day after the acquittal, neighbour Fiona Cunney put her house up for sale. It sold within a week and Leung was finally able to go home.

He must have been mightily relieved, believing his torment was over, but 28 days later, he was in for a nasty surprise. He became the first person to be retried under the new double-jeopardy laws that had been introduced in NSW in 2006, in which the Office of the Director of Public Prosecutions (DPP), under its own volition, can appeal a verdict directed by a judge.

In April 2011, with no new evidence, Leung again faced trial, this time for manslaughter in what was always a circumstantial case. The juicer bowl had Guzzetti's DNA on it, but according to Leung, it was "typical of Mario to pick it up and finish cleaning it".

Justice Rothman had told the court that "the injuries on the deceased could include contact with the metal juice extractor, either at the bottom of the stairs or because the deceased was holding it and came into contact with it on the way down the stairs or at the bottom of the stairs".

There was no financial motive for the alleged crime. The house had been bought in both names. Johnson believes the rest of Guzzetti's estate may have been willed to charity but this is not confirmed. Leung has never made any move to find out what was in the will. Guzzetti's brother Enzo, who took Mario's ashes to Italy without the permission of his life partner, was subsequently brought back to Australia three further times by the prosecution. But Guzzetti's friends say Mario had been estranged from Enzo for 15 years because he didn't like his wife, and had never told Enzo he was gay. They barely knew each other.

On April 28, in Leung's second trial with still no new evidence, Justice Michael Adams noted that a fall down the stairs did not explain all of Guzzetti's injuries but he "could find no evidence on which a jury could properly convict" and directed a verdict of acquittal. The NSW Police indicated that it would not pursue the matter any further.

As Leung left the court, he told journalists he was "finally free" to move on, as he had become the first person in Australian legal history to twice be acquitted of the same crime as directed by a judge.

Johnson remembers having a coffee with him at the end of the 30-day period the DPP had to appeal. "He was excited, saying, 'Only one more day and it will all be over.' The next day, I got a call and he was crying. The DPP had appealed to have Justice Adams' acquittal overturned." Philip Leung was about to make Australian legal history by being the only person ever to face three trials for the same homicide.

The Office of the Director of Public Prosecutions declined to comment to Good Weekend. Each time, the DPP acted on the last day it could appeal. "It was a psychological game," says Johnson.

Winston Terracini, SC, who acted as defence barrister in all three of Leung's trials, says, "Sadly for Mr Leung, his case is unique."

Living in suspense, constricted by bail conditions necessitating regular visits to the police, and battle-fatigued from fighting for his life, Leung fell into a depression. Peter, his concerned ex-partner, wrote an impassioned letter to the NSW Attorney General: "Mr Leung is, in my opinion, now bordering on a nervous breakdown and is actively seeking psychiatric counselling due to ongoing harassment."

Peter says now: "In the past six years, he has been to hell and back. He has had a guillotine blade just waiting to come down and chop his head off." Behaving entirely out of character, say friends, Leung told his psychiatrist that he used alcohol and illicit substances for the first time in his life, and could not sleep.

Last November, a traumatised Leung faced his third trial. Still, there was no new evidence. On November 28, a jury delivered a verdict that had taken two days to reach. Those present say the jury foreman appeared to smile and wink at Leung, which seemed cruel before delivering a verdict of guilty.

Says Johnson, "Philip did not give evidence or make a statement at any of his trials. He chose the right to remain silent. He was relying on the facts to be obvious through lack of evidence, and is still very surprised that the judge at the third trial allowed conjecture and guesswork to influence the jury."

In his sentencing on March 8 this year, Justice Derek Price took into account the "psychological impact of the fluctuating outcomes of directed acquittals at trial and reversal upon appeal" and sentenced Leung to eight years with a non-parole period of four and a half years.

Enzo Guzzetti declared himself happy with the outcome. "It is a fair sentence. Mario can finally rest in peace."

Leung still bursts into opera, but he now does it in Cessnock Correctional Centre. His friends take turns visiting Leung in prison and put money into his account so he can buy a doona, a kettle and make phone calls. Last month, Johnson visited for three hours. "He was in good spirits, we had a barbecue; it was his best meal for a while," he says. "The cells are plain cement and have little comfort. The food is very plain also.

"They can spend up to 16 hours a day with a cellmate in a cell that is two metres by three metres with bunks, so they are careful not to make enemies. I feel he is sad but not depressed."

The pink house in Alexandria sits empty and silent. The music of Verdi and Puccini no longer spills from the wood-framed windows. If Leung loses his next appeal - the date has yet to be set - his half of the house will revert to the estate of Guzzetti.

Three judges, including the bail judge, found that Philip Leung did not have a case to answer. If their judgment is to be believed, then it is possible that an innocent man is in prison - a hapless test case for a new law.

As he was led from the court after the guilty verdict, a sobbing Leung summed it up this way. "This is wrong," he shouted, "just wrong."

This article originally appeared in Good Weekend. Like Good Weekend on Facebook to get regular updates on upcoming stories and events.