(CNN) -- Two registered sex offenders are accused of raping and killing four women in Southern California while the men were wearing GPS ankle-bracelets, authorities say.
"The GPS was in fact intact, attached to these suspects during the commissions of the crimes," Anaheim Police Chief Raul Quezada told reporters Monday.
Steven Dean Gordon, 45, and Franc Cano, 27, were scheduled to be arraigned Tuesday, but the hearing was postponed until May 19 at the request of a defense attorney, authorities said. The two men were arrested Friday night.
Their ankle monitors and the women's cell phone records helped authorities link the cases to the suspects, police said.
The body of Jarrae Nykkole Estepp, 21, of Oklahoma, was found at an Anaheim recycling plant on March 14, Anaheim police said.
The disappearances in Santa Ana of the three other women are being treated as homicides, although their bodies have not been found.
Kianna Jackson, 20, was last reported seen on October 6; Josephine Vargas, 34, on October 24; and Martha Anaya, 28, on November 12.
Both men had been convicted of sex crimes involving children: Gordon in 1992 and Cano in 2007. Each man had checked in with police every 30 days, as required, and authorities had no reason to watch them more closely, Anaheim Police Department spokesman Lt. Bob Dunn said.
A state Department of Corrections official would not say what authorities may have known about the suspects' activity. "Due to the complexity of the investigation, we are not at liberty to speak on those, but, however, the questions are coming forth to headquarters in Sacramento and, as time permits or we're allowed to, they will respond to your questions," Charles Dangerfield told reporters.
All the women are believed to have worked as prostitutes, police said.
CNN's Michael Martinez and Stella Chan contributed to this report.