Investigators have so far linked nine cases -- the first occurring in Chino Hills in 2003 and the most recent in Riverside in 2009 -- to the same suspect through the use of DNA evidence, video surveillance footage, and other evidence, the Los Angeles Times reported.
However, authorities say the suspect, whose identity has not yet been determined, but has been charged by the Riverside County district attorney's office with 31 felonies, including kidnapping, assault with a firearm, forced oral copulation and rape, likely carried out other attacks.
In all of the attacks, which targeted small businesses with immigrant employees, the suspect entered the massage parlor or spa and somehow gained access to a back area.
Then he threatened employees with a gun or knife and forced women to disrobe. In some cases he sexually assaulted multiple women.
He then "severely beat the victims," before robbing them, said Riverside Police Detective Aurelio Melendrez.
The suspect then told the victims he would kill them if they called the police, Melendrez said.
"There are aspects of shame, and we believe there are other victims out there," said Riverside Police Chief Sergio Diaz.
"We don't think he has stopped," Melendrez said.
Police have released a photo of the suspect, described as a man in his 40s, weighing between 240 and 260 pounds, and being about 6 feet tall.
"He's capable of great violence," Melendrez said. "It's repulsive."