Portland, Ore. ? A man who used an Internet chat room to try to set up a mass suicide on Valentine’s Day had been trying to persuade women for at least five years to engage in sex acts with him and then kill themselves, a sheriff said Sunday.

Gerald Krein is charged with solicitation to commit murder, and prosecutors are expected to add an attempted manslaughter charge today, said Klamath County Sheriff Tim Evinger.

Combing through old chat room records, investigators discovered that Krein had been trying to entice women across North America to commit suicide as far back as 2000, Evinger said. Krein told investigators he had been in touch with 31 women, authorities said.

Krein, 26, was arrested Wednesday at his mother’s home in the southern Oregon town of Klamath Falls. He moved to Oregon about a year ago from the Sacramento, Calif., area to take care of his ailing father, Evinger said.

“The common theme is that these were women who were vulnerable, who were depressed. He invited them to engage in certain sexual acts with him — and then they were to hang themselves naked from a beam in his house,” the sheriff said.

Klamath County Prosecutor Ed Caleb said no one knows for sure whether Krein intended to bring participants to his home or conduct the suicide over the Internet. Because Krein was living in a mobile home while organizing the suicide, the idea of hanging bodies from beams may indicate the plot was a fantasy.

No deaths had been found that were linked to Krein, the sheriff said, but he said he would not be surprised if someone had killed herself as a result of Krein’s alleged activities.

Detectives learned of the Valentine’s Day plan from a woman in Ontario, Canada, who said she saw a message in a Yahoo chat room that had “Suicide Ideology” in the title. Chat room participants supposedly planned to commit suicide on Valentine’s Day, possibly while logged on with one another. The chat room is no longer active.

The woman told detectives she was going to take part in the suicide but had second thoughts when another chat room participant talked about killing her children before taking her own life, Evinger said earlier.

So far, investigators have tracked down four of the women Krein was in contact with.