The murders have led Japanese authorities to monitor and crack down on websites where people post about suicide. Twitter also introduced rules against promoting suicide and self-harm in response to the case.
The male victim was the boyfriend of one of the women who confronted Shiraishi at her apartment about her whereabouts and was also killed.
Lawyers for the accused had argued that the murder charges should be reduced because the victims, aged 15 to 27, wanted to die.
Shiraishi is likely to be sentenced to death if found guilty. The perpetrators of multiple murders, robberies or rapes in Japan are usually executed, which is done by hanging.
The accused was arrested in October 2017 when the brother of one of the victims found messages from Shiraishi as he searched his Twitter account after his disappearance. He asked an acquaintance to contact Shiraishi and set up a meeting, then notified the police.
When the police went to Shiraishi’s apartment, he told them that the body of the woman they were looking for was in the freezer. They then found body parts of the nine victims in coolers and other storage containers. He allegedly threw away parts of the body.
“I killed them and worked on the bodies to hide the evidence,” Shiraishi told police, according to the NHK public broadcaster.
Neighbors later told investigators they noticed foul smells coming from the apartment after the accused moved there in August 2017, but reported nothing.
Shiraishi moved to the Tokyo area, where he had worked as a scout recruiting women for the sex industry in Kabukichō, the largest red light district in the Japanese capital.
The defendant opened a Twitter account in March 2017 “to contact women considering suicide, whom he considered easy targets,” according to prosecutors.
The suicide rate in Japan has been declining from a peak in 2003, although there have been a number of high-profile cases this year. Actor Yuko Takeuchi, 40, was found dead at his home on September 27 after what was reportedly suicide.
Shiraishi is expected to be sentenced on December 15.
• In Japan, Tell Lifeline can be contacted at 03-5774-0992. In the United States, the national suicide prevention hotline is 1-800-273-8255. In the UK, Samaritans can be reached on 116 123. In Australia, the Lifeline Crisis Support Service is on 13 11 14. Hotlines for other countries are available here.