Two parolees raped and killed at least four women in Orange County last year while wearing GPS ankle bracelets, police said Monday.

Franc Cano and Steven Dean Gordon, both registered sex offenders, wore the tracking devices and checked in with police every 30 days during the murders last October and November, Anaheim police Chief Raul Quezada said at an afternoon press conference.

The two men were each charged Monday with four felony counts of special circumstances murder and four felony counts of rape, Orange County District Attorney Tony Rackauckas said.

Investigators got a break in the case when a woman's body was discovered on a conveyor belt at an Anaheim recycling plant on March 14. She was later identified as 21-year-old Jarrae Nykkole Estepp of Oklahoma.

The three other women had been reported missing from Santa Ana. They were identified as 20-year-old Kianna Jackson of Las Vegas, and Santa Ana residents Josephine Vargas, 34, and Martha Anaya, 28. Investigators were searching for their bodies.

Quezada said the women’s cases were tied together based on their lifestyle, location and pattern of behavior, including drug use and prostitution in Anaheim and Santa Ana.

Investigators were searching for additional victims. They're also looking into whether an unsolved murder near Costa Mesa last year is connected to the case.

"We are confident there is one additional victim, and possibly more," Quezada said.

Cano, 27, and Steven Dean Gordon, 45, who police said are both transients, were arrested Friday in Anaheim.

If convicted, they face life without the possibility of parole or the death penalty, Rackauckas said.

"Our hearts go out to the victims in this case," Rackauckas said. "Certainly, the families are all very distraught and concerned."

Herlinda Salcedo said police came to her home Saturday to inform her that her daughter Anaya, who disappeared in November 2013, was dead. Police also told her they had not found Anaya’s body.

Salcedo spent months searching for her daughter. The mother told NBC4 she has found closure.

A woman in an area of Santa Ana known for prostitution told NBC4’s Gadi Schwartz that she recognized Gordon, and that he was known to offer women rides in an RV where they could get high on crack cocaine.

“He was always offering rides,” said the woman, who did not want to be identified. “In a safe place, that’s priceless for some of these girls out here.”

Police are in possession of the RV. Arraignment on Tuesday was postponed to May 19.

The Associated Press contributed to this report.