Many young Japanese take to Twitter to discuss suicidal thoughts, and at least nine fell prey to a mass murderer.

Osaka, Japan – Acting on a tipoff, Japanese police knocked on the one-bedroom apartment of Takahiro Shiraishi to inquire about the whereabouts of Aiko Tamura, who went missing a few days earlier in a suburb of Tokyo.

What the police found inside on October 31 was the habitat of a serial killer: a saw, rope, and dismembered body parts of nine people – including severed heads stored in cooler boxes.

Shiraishi – an unemployed 27-year old – had at one stage worked as a scout for female escorts. He lured the women to his apartment, all of whom he befriended on Twitter, with promises of suicide pacts.

The women, whose ages ranged from 15-25, had all expressed suicidal thoughts on the social media platform.

Over a period of three months beginning last August, Shiraishi pored over messages from female users who expressed their willingness to die.

Shiraishi was able to exploit the fact that in Japan social media services, especially Twitter, are a space to talk about suicide – a subject that is still largely taboo.

While Japan’s suicide rate reached its lowest in 22 years in 2016, it is still the highest of the G7 group of rich countries [JJ O’Donogue/Al Jazeera]

Tell Twitter

Tatsuhito Hokujo – director of Befrienders Worldwide Osaka, a suicide prevention network – said people who call their hotline often feel isolated.

“They feel like they don’t have anyone to talk with about their problems.”

In such a situation, they might post “I want to die” on social media and look for someone who can sympathise and react to their intentions, Hokujo told Al Jazeera.

It was posts such as these that Shiraishi reacted to, encouraging and coaching his victims before killing them and, in some cases, sexually assaulting them.

Vickie Skorji, director of Lifeline, which is operated by Tell Japan – a suicide prevention network, said because social media is wide open it’s also open to abuse.

“The very thing that’s connecting them [users] with people is also the very thing that’s putting them at risk,” she said.

Xue Dou, a media psychologist at Ritsumeikan University in Osaka, said in Japanese culture identity is tightly regulated with regard to which group you are in – whether it’s at work, school, or at home. Aspects of your personality and identity are revealed and altered in relation to these groups.

Dou noted in media interviews friends of Shiraishi’s victims frequently said they were shocked to learn they were feeling suicidal.

“Most likely these women did not say anything about suicide in front of their friends, instead opting to comment on social media about wanting to die. Social media is somewhere you don’t have to pretend,” said Dou, adding that Twitter, which affords users anonymity, adds a layer of honesty.

Because social media is wide open, it’s also open to abuse [JJ O’Donoghue/Al Jazeera]

For Eri, a 21-year-old part-time worker in Tokyo, Twitter doubles as her diary. She has several accounts but uses a closed network to reveal her true feelings. She has on occasions posted messages such as “Shinitai” (I want to die) and “I’m in pain.”

“My diary-use Twitter is closed so I don’t have to worry about people that I don’t know who might judge me when I post negative things,” Eri said.

Eri, who only gave her first name to protect her privacy, added she avoids revealing too much on her public accounts where she could easily connect with someone she doesn’t know.

In the days following Shiraishi’s arrest as police pieced together the identity of his victims, Twitter updated its rules forbidding the promotion or encouragement of suicide and self-harm.

However, as Jack Dorsey, co-founder and CEO of Twitter, told Japan’s public broadcaster NHK in a November interview, it would be unrealistic to remove all tweets expressing suicidal intentions. Instead Twitter will concentrate on promoting prevention suicide organisations.

Let’s not talk about it

While Japan’s suicide rate reached its lowest in 22 years in 2016, it is still the highest of the G7 group of rich countries. According to Japan’s government, nearly 22,000 people took their lives last year.

Suicide is also the biggest cause of death for 10-19 year-olds, with a spike in suicides at the start of the school year in April and again in September after the summer holidays.

Talking about mental health is still a stigma in Japan, said Skorji. “That makes people that are struggling with these issues very isolated and they have less avenues to talk about them in a healthy environment.”

It also makes people vulnerable.

“This population [of at-risk people] doesn’t need to be vulnerable if we can all talk about mental health safely, particularly suicide,” Skorji said.

She noted discussions about mental health in Japan are still in their infancy.

Skorji pointed to the efforts of the royal family in the United Kingdom, where Prince William and his brother Prince Harry have openly discussed their emotional and mental suffering following the sudden death of their mother as a way to promote mental health awareness and encourage others to talk.

Haruka Iwamoto contributed to this report