Kazunari Saito, a 33-year-old electrician, was arrested Wednesday for allegedly giving Sayaka Nishizawa, 21, sleeping pills and suffocating her in April, a police official in Kanagawa said, speaking on condition of anonymity, citing policy.
Nishizawa contacted the suspect through an Internet suicide site he hosted and paid him the equivalent of US$1,700, according to the official.
Her body was found on April 16 in her apartment in Kanagawa, just south of Tokyo, the official said. Her father found the body and police had been investigating the case after they found a note suggesting suicide, but her cell phone and keys were missing, Kyodo News agency reported.
The suspect told police the woman had asked him to "see through" the dying process, Kyodo said.
Saito set up his site in June in 2006 to give tips on how to commit suicide, the agency said.
Police officials could not immediately comment if his Web site was still functioning.
According to the Yomiuri, Japan's largest daily, the woman wrote him in early April saying: "I want to die, how can I die?"
Saito wrote back: "I will give you lots of sleeping pills. I will help."
It was not clear why the woman wanted to kill herself or why she needed help in doing so.
The police official also confirmed Saito had been arrested on charges of violating the narcotic and psychotropic drug control law. The official could not give other details.
But Kyodo and other Japanese media said Saito was arrested in July and has been prosecuted for allegedly selling sleeping pills to some 10 people through his site. Kyodo said one of them had died and police were investigating.
Japan's suicide rate is among the highest in the industrialized world, and the number of people taking their own lives topped 30,000 for a ninth straight year in 2006.