Nearly two weeks after a man was arrested for killing and cutting up nine people, Japan has vowed a concerted response against "suicide websites".

Takahiro Shiraishi, 27, who was nabbed on Oct 31, has confessed to preying on victims who expressed suicidal thoughts on social networking site Twitter, luring them with suicide pacts to die together.

But he reneged on the pacts, killing and dismembering his victims whom he found using the hashtag "suicide recruitment". Nine heads and 240 bones belonging to his nine victims - eight females and one male aged between 15 and 26 - were found in his Kanagawa apartment on Halloween.

Chief Cabinet Secretary Yoshihide Suga said yesterday that specific steps on clamping down on websites and social media sites that propagate suicide content will be announced next month.

"The use of Twitter - a social networking site that is difficult to monitor - to exploit the cries for help by victims who wrote about committing suicide is despicable," he said. "We will get to the bottom of this crime, and work towards preventing its re-occurrence."

Minister of Internal Affairs and Communications Seiko Noda, in noting that 50 per cent of junior high and 90 per cent of senior high students own smartphones, stressed that utmost efforts will be made to plug any loopholes in Internet regulations.

In the first half of this year, more than 900 people under the age of 18 fell victim to crimes via social media, including sexual crimes such as child prostitution and pornography, National Police Agency statistics show.

Criminal profiler Enzo Yaksic, director of Northeastern University's Atypical Homicide Research Group, told The Straits Times that with increased surveillance, serial killers now "behave in ways that are not typical to how they operated in the past".

He said: "Researchers are beginning to see the dark recesses of the Internet feature prominently in the planning stages of serial murderers, as they utilise it to locate potential victims, research the methods of previous killers, connect with other like-minded individuals, and store records of their activities and achievements."

The Japan Times said in an editorial yesterday that the outright regulation of online messages posted anonymously through accounts using pseudonyms would be difficult.

Further complicating matters is the fact that users may choose to exchange messages directly with each other after the first contact is made.

Shiraishi's spate of murders has sent shock waves across highly wired Japan, a nation with low crime rates but with a seeming propensity for violent crime.

He has been quoted as telling the police that none of his victims "had actually wanted to die", and that he "could not remember any faces after the second victim".

The identities of the nine victims, released by Tokyo police yesterday, included three high school students and one young mother.

Kyodo News said police could not positively identify the victims earlier because of the state of the dismembered parts, which were stored in cooler boxes in Shiraishi's 13.5 sq m apartment.

Police tapped evidence, like bank cards left by victims at his home, as well as GPS-tracking data from mobile phones, for a preliminary identification.

They then collected DNA samples from family members for a confirmation, the report said.