Two sex offenders are accused of raping and killing four women in Southern California while wearing GPS tracking bracelets locked around their ankles, and investigators believe there may be more victims.

Franc Cano, 27, and Steven Dean Gordon, 45, were previously convicted of sexually abusing children under the age of 14.

In 2012, the suspects cut their ankle bracelets and boarded a bus to Las Vegas using fake names. Court documents indicate the men spent two weeks at the Circus Circus Hotel and Casino where the feds found them.

The victims in this new case had worked as prostitutes. The body of one female victim was found on the conveyer belt at a trash sorting facility in Anaheim. The bodies of three other women are still missing.

Cops say data from the men’s ankle bracelets helped catch the suspects, but investigators haven’t explained how the pair managed to rape and kill while under supervision.

Trace Gallagher reported that Cano and Gordon checked in with their parole officers every month. 

Read more from FoxNews.com below and watch Trace Gallagher's report in the video above. 

The Orange County distract attorney's office said Cano and Gordon, who were arrested Friday, were each charged with four felony counts of special circumstances murder and four felony counts of rape. If convicted, the men could face a minimum sentence of life without parole or the death penalty. They were being held without bail and expected to be arraigned Tuesday.

Anaheim police Chief Raul Quezada said the key to the case was the discovery of 21-year-old Jarrae Nykkole Estepp's naked body on the conveyer belt at an Anaheim trash-sorting plant March 14. Estepp is the only one of the suspected victims whose body has been found. Quezada said authorities were confident that there was at least a fifth victim and perhaps more.

The department has contacted other places with missing-persons cases across the country, Dunn said earlier.

The string of disappearances began in October after Kianna Jackson, 20, of Las Vegas, arrived in Santa Ana for a court hearing on four misdemeanor charges of prostitution and loitering to commit prostitution. Her mother said she stopped responding to her text messages soon after she arrived in Santa Ana.

Josephine Monique Vargas, 34, was last seen Oct. 24 after leaving a family birthday party to go to a store. The Los Angeles Times quoted Vargas's mother as saying that her daughter had a rough past that at times involved drug use and prostitution, but had been trying to better her life.

Martha Anaya, 28, asked her boyfriend to pick up their 5-year-old daughter so she could work on Nov. 12, then stopped responding to his messages later that night. Police said she also had a history of prostitution.

The Associated Press reported that in the weeks prior to her death, Estepp had become a regular on a strip of Beach Boulevard in Anaheim long known for prostitution.

Police at first didn't link the disappearances of the four women to the suspects, considering them missing persons rather than murder victims.

"These individuals were not on our radar whatsoever," Santa Ana Police Chief Carlos Rojas said of the suspects. "Our three missing in Santa Ana just completely went off the grid and we were trying to follow up as much as we could."

Santa Ana police searched a canyon, examined the women's cellphone records, alerted hospitals, put the word out on social media and even checked motels they were known to frequent but without success in finding them.

Once investigators concluded that Estepp was killed and that she had "a similar profile to our victims, we were able to ... move forward," Rojas said.