A Japanese man dubbed as “Twitter killer”, pleaded guilty to murdering nine people after contacting them on Twitter.
Takahiro Shiraishi was arrested in 2017 after body parts were found in his flat, the revelation shocked Japan.
He told a court in Tokyo on Wednesday that the allegations against him “are all correct”.
But his lawyers argue that his charges should be reduced because his victims apparently gave consent to be killed.
If convicted of murder, Mr Shiraishi faces the death penalty, which is carried out by hanging in Japan.
The prosecution say the accused opened a Twitter account in March 2017 “to contact women contemplating suicide, whom he saw as easy targets”, NHK said.
Eight of his victims were women, one of them aged 15.
The only male victim, aged 20, was killed after confronting Mr Shiraishi about the whereabouts of his girlfriend, Japanese media reported.
The 29-year-old is believed to have lured his victims by telling 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.”
The serial killings first came to light when police were looking into the disappearance of a young woman, who later turned out to be one of the victims.
Officers visited Mr Shiraishi’s flat in the Japanese city of Zama, near Tokyo, where they found dismembered body parts.
The court case has attracted wide interest, with more than 600 people lining up for 13 public gallery seats to watch the first hearing on Wednesday, reported public broadcaster NHK.
The murders also prompted a change by Twitter, which amended its rules to state users should not “promote or encourage suicide or self-harm”.
Twitter’s chief executive Jack Dorsey said at the time the case was “extremely” sad.
Japan has long battled one of the highest suicide rates in the industrialised world although figures have dropped since preventative measures were introduced more than a decade ago.
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