Sef Gonzales was born in Baguio, Benguet, Philippines to Teddy and Mary Loiva Gonzales. After the 1990 earthquake destroyed their hotel business (his father rescued him when the hotel collapsed), Teddy Gonzales and his family emigrated to Australia, where Teddy worked as an immigration lawyer. The Gonzales family appeared to be close-knit: the parents were strict and devout Catholics who had high hopes for their children. Later, court evidence suggested that the Gonzaleses enforced harsh discipline on their children when they did not meet their parents' high expectations. In particular, they had hoped Sef would perform well academically, and have a career in medicine or law.
After secondary school, Gonzales attended the University of New South Wales, where he stayed in Warrane College for a time. Performing poorly in his courses and at risk of expulsion, he tried to cover up his academic failure by falsifying his results, but when this was discovered by his parents they threatened to withdraw certain privileges, such as the use of his car. He had also argued with his mother over a girlfriend of whom she disapproved, and his family had threatened to disinherit him. This, along with Sef's desire to inherit the family's fortune (about AU$1.5 million), were established by police as his motives for killing his parents and sister.
On 10 July 2001 at about 4:30 p.m., Gonzales entered Clodine’s bedroom in the house at 6 Collins Street, North Ryde, where she was studying. He was armed with a baseball bat or similar item and with two kitchen knives he had taken from a knife block in the kitchen. It was found that he compressed Clodine’s neck trying to strangle her, struck at least six separate blows to her head with the bat, and stabbed her many times with one or both of the knives. He inflicted five major stab wounds to Clodine’s neck and two major stab wounds to her chest or abdomen. The cause of Clodine’s death was the combined effect of the compression of her neck, the blunt force head injuries and the abdominal stab wounds.
Mary Loiva arrived home about 5:30 p.m. After entering the house, Sef attacked her with one of the kitchen knives in the living/dining room. Gonzales inflicted multiple stab wounds and cuts to her face, neck, chest and abdomen. Her windpipe was completely transected in the attack. Teddy arrived about 6.50pm. After entering the house, Sef attacked him with one of the kitchen knives and inflicted multiple stab wounds to his neck, chest, back and abdomen. One of the stab wounds penetrated his right lung, another penetrated his heart and another partially severed his spinal cord. Teddy sustained defensive wounds, suggesting that there was a struggle.
After killing his family, Gonzales disposed of the murder weapons, including the bat he had used in striking Clodine, and the shoes and clothing he was wearing at the time of the murders, which had become blood stained. He showered, changed clothes, and at some time during the evening, spray painted the words "Fuck off Asians" on a wall in the house in an attempt to fool investigating police into believing that his family had been the victims of a hate crime. Gonzales' clothes were later found to have the same paint used in the graffiti scrawl.
After committing the murders, Gonzales drove to a friend's house, arriving there about 8pm. Sef and his friend Sam Dacillo (who was not aware of the murders), went to the Sydney CBD, where they went to Planet Hollywood and then to a nearby video game arcade. Later in the evening, after dropping his friend off, Gonzales returned to the North Ryde home. He called police to say he had discovered the bodies on his arrival at the house, and that he had chased off intruders. Gonzales had also frantically run to his neighbours' house and told them that his parents had been shot. In the days following the murders, Gonzales appeared on television asking for the killers to come forward, saying he wanted justice and offering a reward of $100,000 for information, and attracted sympathy when he sang One Sweet Day at the family funeral.
After noticing many inconsistencies in Gonzales' story and no evidence of any intruders, police investigating the murders began to believe that he was the perpetrator. In December, investigating police were able to disprove Gonzales' first alibi, when they were told of sightings of his car in the driveway at the time of the murders. Gonzales then constructed a second alibi, claiming he had visited a brothel at the time of the murders, but this was proven to be false by the prostitute who he claimed to be with at the time.
Other false trails were the fabrication of an e-mail that implicated a business rival of Teddy in the murders, the fabrication of threatening e-mails, and the staging of an attempted burglary and an abduction. A few days after the murder, Gonzales visited the family's accountant, enquiring about his inheritance. During his criminal trial, it was alleged that Gonzales put a deposit on a $173,000 Lexus, telling the dealership he would be using his inheritance to pay for the vehicle. It was also claimed that he traded in his parents' cars and pawned his mother's jewellery. Gonzales also told relatives that he had a brain tumour and asked his godmother in the Philippines for $190,000 for the alleged surgery.
On 13 June 2002, detectives from Strike Force Tawas of the NSW Police arrested Sef Gonzales and charged him with three counts of murder and one count of threatening product contamination. He was refused bail and held in remand in Silverwater Correctional Centre. He was also denied access to the family's estate to fund his defence.
The murder trial took place during April and May 2004. The trial revealed that Gonzales had planned the murders for several months before they took place. Initially Gonzales researched the idea of poisoning his family, which led to an elaborate contamination hoax. The court heard of numerous lies told to his friends, family and police regarding his whereabouts at the time of the murders. It was later suggested that Gonzales was a pathological liar.
It was found that he had committed the murders because he was fearful that, because of his poor performance in his university studies, his parents might take his car away from him and might withdraw other privileges which had been granted to him and that he wished to be the sole beneficiary of his parents' property, estimated to be worth $1.5 million.
On 20 May 2004, the jury found Gonzales guilty of all four charges. He was sentenced on 17 September 2004 (the day after his 24th birthday) to three concurrent life sentences without parole for the murders, Justice Bruce James remarking "I consider that the murders show features of very great heinousness and that there are no facts mitigating the objective seriousness of the murders and hence the murders fall within the worst category of cases of murder at common law." Gonzales is now serving his sentence at the maximum-security super prison in Goulburn, New South Wales, and maintains his innocence.
In June 2007, Gonzales was granted approval to appeal his conviction and his sentence. The Supreme Court determined that statements taken from Gonzales by police on the night of the murders may be inadmissible, as he was not cautioned. On 27 November 2007, Sef Gonzales' appeal was dismissed as there had been no miscarriage of justice, and his convictions remained.
The North Ryde house where the murders took place was put on the market, arousing controversy in October 2004 when the prospective buyers, a Buddhist couple, learned of the home's history. They had not been informed of the events that took place there, finding out from a newspaper only when the balance of the sale value was due. After this incident was publicised the NSW government made it illegal to sell a house without disclosing murders that took place in it. LJ Hooker eventually refunded the buyer's deposit on their purchase due to the bad publicity it caused for LJ Hooker. The real estate company was also fined $21,000. In November 2005, the house was sold for $720,000 ($80,000 less than the initial sale) to a buyer who was aware of its history.