Two parolees raped and killed at least four women while wearing GPS trackers, and there may be more victims, a California police chief said.
Authorities at the news conference did not explain how Cano and Gordon, who are now in custody, allegedly managed to carry out the killings while under supervision, but Quezada said data from the global-positioning system devices "was one of the investigative tools we used to put the case together".
Senior Anaheim officer Bob Dunn earlier said the two were complying with a requirement to check in monthly with authorities and police had no reason to watch them more closely and had not received any such request from other agencies.
Quezada said authorities were sure there was at least a fifth victim and perhaps more, with authorities seeking details on missing persons.
Police believe the men killed a woman in Anaheim and three others in Santa Ana last October and November while on parole.
Cano, 27, and Gordon, 45, were arrested on Friday. Each was charged with four counts of murder and four counts of rape.