Japan has executed a man who murdered nine people in 2017, the first time since 2022 that the country has enacted capital punishment.

The serial killings by Takahiro Shiraishi, dubbed the "Twitter killer", had shocked the country and triggered debate over how suicide was discussed online.

Shiraishi, then 30, lured his victims - most of them young women between the ages of 15 and 26 - to his apartment, before strangling and dismembering them.

The killings came to light in October 2017, when police found body parts in the Japanese city of Zama, near Tokyo, when they were searching for one of the victims.

Warning: Readers may find some details in this story distressing.

Shiraishi later admitted to murdering nine suicidal victims and revealed that he got acquainted with them on Twitter, the social media platform now known as X.

He then told them he could help them die, and in some cases claimed he would kill himself alongside them.

His Twitter profile contained the words: "I want to help people who are really in pain. Please DM [direct message] me anytime."

Nine dismembered bodies were found in coolers and tool boxes when officers visited his flat, which was dubbed by media outlets as a "house of horrors".

While prosecutors sought the death penalty for Shiraishi, his lawyers argued for the lesser charge of "murder with consent", claiming his victims had given their permission to be killed.

They also called for an assessment of his mental state.

Shiraishi later disputed his own defence team's version of events and said he killed without the victims' consent.

Hundreds of people showed up at his verdict hearing in December 2020, when he was sentenced to death.

The murders also prompted a change by Twitter, which amended its rules to state users should not "promote or encourage suicide or self-harm".

Japan's justice minister Keisuke Suzuki, who said he ordered Shiraishi's execution, said the killer acted "for the genuinely selfish reason of satisfying his own sexual and financial desires", according to an AFP report.

The case "caused great shock and anxiety to society", Suzuki said.

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