In June, one month after he was given a suspended prison term for being a scout for a prostitution ring, Takahiro Shiraishi told his father that he saw no meaning in life.
Jobless, the 27-year-old cocooned himself further in the dark recesses of social media. He used Twitter, a medium he once used to lure girls into the sex trade, to meet people with suicidal thoughts.
The gruesome Halloween find of nine human heads and 240 bones in his studio apartment in Zama city, an hour and a half from central Tokyo, has spooked Japan and again shone a light on suicide and mental health issues in a country that even has a "suicide forest".
Japan has the sixth highest suicide rate in the world. Some 21,897 killed themselves last year - a 22-year low, while there were 257 reports filed with the Internet Hotline Centre about suicide attempts.
Shiraishi grew up in Zama with his parents and a younger sister in a house roughly 2.5km from his loft apartment.
He was a quiet, inconspicuous boy who went to local elementary and junior high schools in the city, acquaintances told Japanese media.
His grades were not stellar, but he was a conscientious student who did not miss a day of school. News pictures show a scrawny teenager with thin-rimmed spectacles who joined his junior high's baseball team as a freshman, and then the track team as a senior.
He went on to study at the prefectural high school in the city of Yokohamaand it was around this time that things fell apart at home. His parents divorced, and his mother and sister moved out.
After graduating from senior high, Shiraishi took on a series of odd jobs - including at a supermarket, food factory and pachinko parlour - before becoming a scout for a prostitution ring.
Shocking murders in Japan
In July last year, the Hitler-influenced Satoshi Uematsu, then 26, went on a stabbing rampage at a home for the disabled in Sagamihara, north of Tokyo.
The attack left 19 dead and 26 others injured in what was the bloodiest crime in post-war Japan.
Uematsu, who was sacked by the facility for his radical thoughts, had said he wanted to "cleanse society of imperfection" - even writing to the Cabinet Office about his ideologies at one point. He remains unrepentant about his crime.
In 2008, Tomohuro Kato, then 26, killed seven and injured 10 others at popular electronics belt Akihabara by ramming his truck into the crowd and then alighting and going on a stabbing spree.
Mired in poverty and sacked from his temporary job, he was filled with pent-up anger.
"I'm lower than trash because at least the trash gets recycled," he wrote on an Internet bulletin board, where he gave blow-by-blow updates of his attack.
OSAKA SUICIDE KILLING
Osaka police arrested Hiroshi Maeue, then 38, in August 2005 for murdering three people whom he had lured on a suicide website.
Maeue, who has been sentenced to death, had agreed to die by suffocation jointly with a 25-year-old woman by burning coal briquettes in a vehicle. He ended up strangling her in the car, and then disposing of her body.
He also killed a 14-year-old male junior high school student and a 21-year-old male undergraduate that same year.
He was active in Shinjuku's seedy Kabukicho district, and was once described as an "ambitious, dangerous man who is capable of betrayal".
One woman, who cohabited with him for three months earlier this year, said Shiraishi was "unusually more gentle than ordinary people" despite a morbid fascination with death and suicide.
He had sent her messages such as "Let's commit suicide together", and once texted "I have killed a hostess who said she wanted to die", which the former girlfriend dismissed as a joke.
Shiraishi was close to his father, who works at an automotive design workshop, neighbours said. The son frequently helped out at the workshop, and occasionally had dinner and drinks with his father.
In August, he confessed to his father that he had met the love of his life and would urgently like to have his own space. His father acted as guarantor for an apartment in the neighbourhood that rents for 19,000 yen ($227) a month.
On Aug 22, Shiraishi moved into the 13.5 sq m apartment which Japanese media has described as the "house of horrors".
While living on his own, Shiraishi built up a small following on Twitter through at least two accounts - "I want to die" and "A professional at hanging".
Under the first account, he cast himself as a forlorn victim seeking company for his misery. "I want to forget everything," he wrote in an Aug 25 post. "I want to disappear."
Under the second account, he took on the persona of someone who is skilled at helping people die. "I want to spread my knowledge in hanging," he said. "I really want to become the source of strength for everyone who is in pain."
"If you are at a dead end, please consult me," he wrote.
He also sought out his victims using the hashtag "suicide recruitment" on Twitter, preying on young girls who wanted to take their own lives. He told them via direct messaging on Twitter: "Let's die together."
To ensure his victims would not back out at the last minute, he would arrange to meet them at a train station near their homes, then travel together to his apartment.
He said he gave them alcohol, tranquilisers and sleeping pills "to make them relax", before assaulting them.
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He confessed to killing one person in August, four in September and four in October - mostly on the same day he met them. Eight of the nine victims were women, mainly in their late teens to early 20s.
"It was difficult at first. It took me three days to get rid of the first body, but after that I could deal with them within one day," Shiraishi told the police.
GOT USED TO IT
It was difficult at first. It took me three days to get rid of the first body, but after that, I could deal with them within one day.
TAKAHIRO SHIRAISHI, speaking to the police.
He said his motives had been sex and money. He is alleged to have choked his victims - whose real names and ages he did not know - until they passed out, before sexually assaulting some of them.
"There is no doubt that I sliced up the bodies in my bathroom with the intention of destroying evidence," he said.
Police have recovered two kitchen knives, scissors, a saw, binding rope and a gimlet, all with traces of blood on them.
Shiraishi said: "I disposed of their flesh and internal organs like garbage, but kept their bones out of fear that I would be caught."
Police also found three cooler boxes and five large storage boxes in his apartment. They checked the eight boxes and found body parts, including heads, legs and arms, in seven of the boxes.
He reportedly used cat litter to cover the body parts to mask the smell.
His neighbours in the two-storey, 12-unit apartment block said they had neither seen nor heard anything amiss, despite complaints of a persistent "pungent smell" emanating from his apartment.
One of them pointed out that it was strange that his bathroom ventilation fan was kept on at all times.
Shiraishi even brazenly used the neighbourhood garbage collection point to dispose of the evidence. A neighbour has noted - in hindsight - his frequent trips to the chute.
It was the online trail he left on social media which eventually led the police to his doorstep.
The brother of his ninth and final victim - a 23-year-old woman from the Tokyo suburb of Hachioji - hacked into her Twitter account, and was offered help by a woman who had met Shiraishi before.
She agreed to be the bait to lure Shiraishi out for the police, who then followed him home on Oct 30.
When asked if he knew where the missing 23-year-old woman was, he pointed at a chiller box near the entrance and said: "In there."