TOKYO — A Japanese court on Thursday sentenced to death a man who had confessed to stalking and murdering women who had expressed suicidal thoughts on social media, bringing an end to a grisly case that played to many of the country’s social anxieties.
The court in Tokyo said the sentence against Takahiro Shiraishi, 30, was prompted by the “extreme seriousness” of his crimes. Mr. Shiraishi, a judge said, had not just murdered his victims but had “trampled on the dignity of the dead.”
At a sentencing hearing in November, some members of the victims’ families said that they had been irreversibly scarred by Mr. Shiraishi’s actions and his utter lack of remorse on the stand had convinced them that he should be put to death.
The brother of one victim said that listening to Mr. Shiraishi describe his crimes had made him lose faith in humanity. The names were withheld to protect the victims’ privacy.
Executions in Japan are relatively rare, though it remains one of the few developed countries that still enforces the death penalty. Last year it executed three people, according to Amnesty International, a human rights group that criticizes the practice, compared with 22 in the United States.
Mr. Shiraishi, nicknamed “the Twitter killer” in the English-language media, had confessed to meeting eight women over social media and preying on their insecurities to lure them into meetings over a two-month period. He drugged them, sexually assaulted and then killed them to stop them from reporting him to the police.
He later killed an acquaintance of one of his victims after he began to fear that the man suspected him of murder.
The murders have horrified Japan since the police discovered nine mutilated, decomposing corpses in Mr. Shiraishi’s apartment in 2017.
Violent crime of any kind is a rarity in Japan, and grisly murders like those committed by Mr. Shiraishi even more so.
The details of the crimes evoked some of the country’s widely discussed social ills: the erosion of family ties, high suicide rates and an increasingly atomized, isolated society that has turned to social media for cold comfort.
Police officers discovered the bodies of Mr. Shiraishi’s victims in his apartment outside of Tokyo after the disappearance of a 23-year-old woman who had posted on Twitter that she was looking for someone to kill herself with.
After setting up a sting operation, investigators followed Mr. Shiraishi to his apartment, where they discovered the bodies of eight women and one man with their heads removed and put in coolers.
Mr. Shiraishi later testified that he had at first considered denying his involvement but changed his mind in the face of the overwhelming evidence against him.
Mr. Shiraishi’s defense attorney had argued that the women were suicidal and that they had agreed to let Mr. Shiraishi murder them, a scenario that would have qualified him for a lighter sentence.
But Mr. Shiraishi flatly rejected the defense, testifying during earlier court appearances that he killed the women of his own accord and wanted to take full responsibility for their murders.
“Not a single one of my victims consented,” he told the judge during one such session.
He has said that he did not plan to appeal his sentence, noting that he had told his defense attorney that he wanted the trial to be over as quickly as possible to avoid causing additional hardship for his parents.
In statements to the court, Mr. Shiraishi traced the motivations for his crimes back to a falling out with his family.
After arguing with his father, he decided to try making a living by seducing lonely women and convincing them to give him money.
Mr. Shiraishi said that he had learned to prey on women’s insecurities while working as a recruiter for an escort service in Kabukicho, a red-light district in Tokyo. While prostitution is illegal in Japan, sex-related businesses — ranging from hostess clubs to massage parlors — are common in urban areas, and young men are often hired to comb city streets for potential employees.
Mr. Shiraishi said he had searched for women online who expressed suicidal thoughts, met up with them and plied them with compliments.
Mr. Shiraishi turned to murder after he began to fear that one of the women he met would demand that he repay money she had lent him.
He was serving a suspended sentence related to his previous work — he had knowingly and against the law recruited women to work as prostitutes — and, imagining that the woman could take the case to the police, he killed her, he said.
“I had a hard time making up my mind to do it, but I had done illegal things on a daily basis as part of my work as a scout and had internalized the idea that ‘It’s only a problem if you get caught,’” he told the court.
After the first murder, he said, the rest were easy.
In a court appearance, Mr. Shiraishi said that, while he felt bad for some of his victims, he had little remorse.
“If they hadn’t caught me,” he said, “I would regret nothing.”
Hisako Ueno and Hikari Hida contributed reporting.