It might be due to the fact that the known victims were vulnerable. Quite often, vulnerable victims receive far less attention. Using online dating sites to meet women - including one who lived in California - might mean that victims are in other parts of the country with no easy way of connecting the suspect to the victims.
Israel Keyes made sure that he left on trace when he flew around the country for the sole purpose of committing murder. Perhaps the suspect was more cautious in the past about distancing himself from the murders.
