"This is a possible homicide. This is a crime scene. And, so, the evidence that they're looking for is anything ... anything at all," said Steve Whitmore, Los Angeles County Sheriff's Department.
The Los Angeles County Sheriff's Department believes Jonathan and Linda Sohus were murdered. They were living at the home on Lorraine Road when they vanished.
"Hopefully we can wrap this up. It's going to take some time, it's meticulous right now. Forensic work is delicate and it takes time and thoroughness is a premium," said Whitmore.
The search for the missing couple has resurfaced after an arrest of a man who calls himself "Clark Rockefeller."
"He is the person who was renting the back guest house at the time of their disappearance. And he disappeared shortly after the time that the couple disappeared," said Whitmore.
Fingerprints identify Rockefeller as Christian Gerhartsreiter, a German national who has been in the U.S. for nearly three decades.
Gerhartsreiter was known as "Christopher Chichester" when he lived in San Marino.
Detectives have tried to question him about the case, but he's not talking.
Investigators were digging, hauling and sifting through the dirt to look for the remains of a newlywed couple who disappeared 23 years ago.
Investigators brought in cadaver dogs to sniff for clues. They also brought radar equipment to scan the ground for anything unusual.
"It cannot tell you what it is, but it can tell you if it probably doesn't belong ... an anomaly if you will," said Whitmore.
Investigators aren't saying whether or not they found any evidence in the back yard on Friday. However, they are covering every inch of that yard and they told Eyewitness News the day was productive.
"We came back here one last time to make sure ... using everything available to us today ... that we didn't overlook anything. So we're going to stay here until the job is done. And then, hopefully, the goal is we don't come back," said Whitmore.
One city block in San Marino was shut down during the investigation.