SAN DIEGO -- Two murder investigations with two very similar stories are now in full stride.

While local authorities are saying very little, they did bridge the gap between the Chelsea King case and the Amber Dubois case by declaring sex offender John Garder -- accused in the death of King -- a focus of the Dubois investigation.

Sheldon Zhang, who studies criminal patterns at San Diego State University, told 10News, "Kidnapping, kidnapping teenagers in this case, Chelsea King's case … it's a sign there's a sex offender out there, not just random serial killers."

Zhang said by looking at the information available, it can be predicted that both crimes were committed by people who wanted to do more than just kill their victims. He said if they just wanted to kill, they may have picked someone other than teenage girls.

"There are a lot easier targets," Zhang said.

Zhang said it's easy to look at the King and Dubois cases and think they are connected. While that may or may not be true, he said what is true is that whoever killed both girls has similar taste in victims.

"Just look at their faces. They're in the prime age; they're prime targets for sex offenders. My hunch is that both cases involve sex offenders, but whether these two cases are connected, I have no idea," said Zhang.

If the cases were committed by a serial killer, it would not be the first time that has happened in San Diego County.

One of the most notorious San Diego serial killers was Cleophus Prince Jr., who was given a death sentence in 1993 for killing six women.