Takahiro Shiraishi, the man who used Twitter to facilitate his gruesome murders was sentenced to death on Tuesday.
With the help of Twitter, he used to lure suicidal women to his home where he drugged, robbed, raped, and killed them before dismembering their bodies, reports The Straits Times, a Singapore based daily.
On Halloween in 2017, police discovered nine human heads and 240 bones stored in cooler boxes at his apartment.
The Japanese media later termed his house in Zama city, 90 minutes from central Tokyo, as the ''house of terrors.''
The nine murders took place over the span of three months from August to October 2017.
Eight of the victims were women aged 15 to 26.
The only man was an acquaintance of one of the missing women and was killed when he came too close to discovering Shiraishi's crimes.
Shiraishi, now 30, pleaded guilty to all the charges against him during his trial, which spanned 23 hearings and centred on his degree of culpability.
His defence lawyers argued that the murders were "consensual" and should amount to the lesser charge of homicide with consent.
"None of the victims agreed to be killed. The defendant was found to be fully responsible," Presiding Judge Naokuni Yano said on Tuesday as he sentenced Shiraishi to death.
In media interviews leading up to the verdict, he had complained that the process was taking too long and that he would gladly accept the death penalty.
During his trial, he apologised to some of the bereaved families who took the stand, though he would not meet their eyes.
"I am sorry for having killed some of the victims, with whom I spent a lot of time, and would like to apologise to these families."
But he had also been defiant: "But for the others, I don't really feel a deep sense of regret. In any case, I am sorry only because I failed when I got caught. If I wasn't arrested, I will not be regretting anything."
Once a scout for the seedy sex industry in Shinjuku's Kabukicho district, Shiraishi had a flair for sweet-talking young women into doing his bidding.
Jobless and aimless in 2017, he adapted these techniques to seek out suicidal women using two Twitter accounts.
In one, he posed as a suicide guru skilled at helping people end their lives. In the other, he cast himself as a forlorn man who wanted company for his misery, seeking out others with whom he can enter into suicide pacts.
To ensure his victims would not back out at the last minute, he arranged to meet them at a train station near their homes before travelling together to his apartment.
There, he fed them alcohol, tranquillisers and sleeping pills, before assaulting and raping them.
He killed his first victim, a 21-year-old woman after she demanded the return of a loan. His subsequent victims, he said, were murdered because he feared they would report his sexual assault on them.
"There is no doubt that I sliced up the bodies in my bathroom with the intention of destroying evidence," he once told police investigators. "I disposed of their flesh and internal organs like garbage, but kept their bones out of fear that I would be caught."
Shiraishi was found out only when the brother of the ninth and final victim hacked into her Twitter account and uncovered the disturbing messages.
The prosecutors said in closing arguments that Shiraishi's crimes "deserve death", adding: "Nine young lives were taken in such a short span of two months."
They added that it was impossible to conclude that the victims consented to be killed, given their resistance to being strangled as well as statements indicating their will to live made to their relatives before they met Shiraishi.
Shiraishi's defence team argued that tacit approval was given through the Twitter message exchanges and that the resistance had amounted to "conditional reflexes" to being strangled.
The defence lawyers also argued that Shiraishi could have been mentally unstable or in a state of diminished capacity at the time, though prosecutors disagreed with this assessment as Shiraishi had been found to be mentally sound after five months of psychiatric tests.
Shiraishi himself, however, has said: "I killed them for financial reasons and to satisfy my sexual desires. There was no consent."
Accusing his own defence team of an "act of betrayal", he repeatedly refused to answer questions from his lawyers and instead said that the "content of the indictment is true".
He has said: "I have said repeatedly that I will accept the indictment and want to end the trial as soon as possible because it is causing inconvenience to my relatives, but this wish is being ignored."