He studied his victims for days, perhaps weeks, learning their names, their addresses, their habits. He found when the women would be vulnerable, then attacked them in their homes.
During the assaults, some lasting hours, he covered their eyes and mouth with duct tape, bound their hands and ankles, and talked to them in an easy, conversational tone.
Investigators now believe at least nine such rapes and one attempted rape over the past 15 years in Northern California are linked to one man. He struck again last month by raping two women in Sacramento.
Police agencies are urgently trying to find him before he attacks again.
"The words are the same, the duct tape is the same," Davis Police Sgt. Scott Smith said Wednesday.
Frustrated detectives linked several rapes in the 1990s to the same attacker through his DNA but have not been able to match it to anyone in DNA databases.
"I don't know whether this guy has been lucky or good" at concealing his identity, Chico Police Sgt. Dave Barrow said.
The rapist struck in that north-central California college town in 1997.
Break in the case?
Investigators think the rapist recently might have made enough mistakes to allow identification.
In his latest attack, Oct. 13, he spent six hours raping two women, ages 24 and 28, in their home in Sacramento's North Natomas neighborhood, Sacramento Police Detective Paul Schindler said.
One of the victims walked past his vehicle while it was parked in her garage, after he already had broken into the house and assaulted her roommate. A neighbor's security camera caught the same vehicle as it drove by. Police described it as a 2001 or 2002 white Toyota 4-Runner with silver molding, a moon roof and roof rack.
Moreover, the victims were able to give police their first recent description of the rapist.
He has put on 30 to 40 pounds since his attacks began years ago and developed a noticeable pot belly as he has aged. He is described as white, 37 to 40 years old, 200 to 250 pounds and five foot-eight to six feet tall.
More than 30 tips were reported to Sacramento police after they publicized a police artist's sketch and vehicle description earlier this week, Schindler said. As a result, they also are linking the same man to a 1996 attempted rape in Woodland.
All his known victims since that year have been Asian women who were attacked across a broad swath of Northern California: Sacramento, Davis, Chico and Martinez. His first known victims, in Rohnert Park in 1991 and Vallejo in 1992, were white.
Knife, gun, disguises
During his attacks, the man has threatened his victims with a knife or a gun and often wears disguises.
After raping two women in Davis in 1997, he was photographed wearing a clear, form-fitting hockey mask while using one of the victim's debit cards at a Woodland ATM.
On Halloween 1996, he approached a woman's home in Martinez while wearing a skeleton mask. When she opened the door, he forced his way in, raped her and stole her ATM card. About three weeks later, he called her at work to apologize.
"He's a pretty demented person that he would somehow think that the victim would enjoy that," Martinez Police Detective Sgt. Gary Peterson said.
Police are puzzled by the apparent six-year gap between a rape in Davis in 2000 and last month's double rape in Sacramento.
"You can speculate forever on that," said Smith, the Davis police sergeant. "Was he in custody? That doesn't seem likely because we'd have his DNA. Was he out of state? Was he inactive? Or were there more attacks ... and we just don't know about them?
"The consensus is he didn't just quit for six years."
Other states are checking their own DNA databases and looking for similar rapes, he said.
Serial rapists sometimes halt their assaults for a period of years because they fear discovery or because their personal circumstances change so they don't feel the urge, said Jack Levin, director of the Brudnick Center on Violence and Conflict at Northeastern University in Boston.
The Northern California rapist, he said, psychologically tortures his victims.
"He tells them he stalks them; he makes phone calls to them later. He's saying, 'I'm watching,'" said Levin, who is not involved in the investigation. "He terrifies his victims so they think, 'Hey, he may come back.'"