A convicted sex offender charged with raping and killing four Southern California women while he wore an electronic monitor was a predator like the shark in the movie "Jaws," the prosecution said on the trial's opening day Wednesday.

In his opening statement, Orange County Deputy District Attorney Larry Yellin said GPS and mobile phone data was used to track down Steven Dean Gordon and another man, comparing it to the hunt for the killer shark.

"'Jaws' is about a predator," Larry Yellin told jurors. "This case is about two. You are about to see the hunt."

Gordon, 47, who is acting as his own attorney, declined to make an opening statement.

He and another sex offender, Franc Cano, 30, were wearing GPS tracking devices for prior offenses when they worked together to randomly target the women in 2013 and 2014, authorities said.

One body was found at a recycling plant while the remains of three other women haven't been found.

Gordon and Cano have pleaded not guilty to rape and murder with special circumstances. Cano's separate trial hasn't started. Both could face the death penalty if convicted.

Relatives of the victims were the trial's first witnesses including Kathy Menzies, mother of 20-year-old Kianna Jackson.

Menzies held back tears as she described her increasing worry.

"I called jails to see if she was there," Menzies said. "I looked online. I even called the morgues."

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Gordon confessed during grand jury proceedings, giving graphic details about picking up the women in his car with another registered sex offender, raping them behind an Anaheim paint and body shop where the men camped, and killing them, authorities said.

But the confession won't be allowed at trial. The judge excluded it because Gordon told police he didn't want to talk before launching into the elaborate account of the killings, Yellin has said.

During the investigation, authorities identified the victim at the recycling plant as Jarrae Nykkole Estepp, 21, from the tattoo on the back of her neck. They searched a database of sex offenders wearing tracking devices and found Cano had been in the locations of all four women when they vanished.

They focused on Gordon after a search of Cano's cellphone showed that the men texted constantly. The night Estepp died, a message from Gordon's phone to Cano's read, "this is the best one yet."

DNA samples from Estepp's body matched Cano's and Gordon's genetic material, authorities said.

Authorities believe Cano and Gordon have known each other since at least 2010, when Cano cut off his GPS device and fled to Alabama, where the men were arrested. In 2012, they cut off the devices again and took a bus to Las Vegas using fake names. They were arrested two weeks later.

Both men are registered sex offenders and were convicted in separate cases of lewd and lascivious acts on a child.