Neighbors identified the house as belonging to Damon Robinson, who has lived next door to the Garridos for more than three years.
Robinson's then-girlfriend in 2006 called police after she saw tents and children in the backyard. The responding officer failed to discover the encampment where authorities say Dugard was kept captive.
Robinson could not be reached after his home was declared a crime scene. He earlier told The Associated Press that Phillip Garrido was the caretaker of the house until Robinson moved there in 2006.
Neighbor Janice Deitrich, 66, also said that Phillip Garrido would visit and help feed an elderly neighbor who lived in the house before Robinson.
Police said the cordoned off property was a crime scene but declined to comment further.
The investigations are "preliminary," said Jimmy Lee, a spokesman for the Contra Costa County Sheriff's Department, east of San Francisco Bay, declining to say what past cases were being reviewed.
Police in Pittsburg are investigating whether Phillip Garrido, whose home is in nearby Antioch, is linked to several unsolved murders of prostitutes in the early 1990s. Antioch police are also looking into unsolved cases but declined further details.
About a dozen agents scoured the modest house and the acre of land it sat on Saturday afternoon as the temperature soared into triple digits.
Police spent most of the day searching the Garridos' backyard, where Dugard is alleged to have lived in tents and shacks with her two daughters fathered by Phillip Garrido. One officer could be seen scanning the backyard with a metal detector while another dug a hole. A third used a chainsaw to clear branches and investigators shuffled in and out of the property all day.
Officers from the Pittsburg Police Department, Antioch Police Department and the Contra Costa County Sheriff's Department were on hand. The agencies say they are reviewing unsolved cases to determine if the Garridos are connected. Pittsburg Police, for instance, said they are looking into whether the Garridos are connected to a string of prostitution murders in that city in the early 1990s. The other agencies declined to discuss what cold cases they were reviewing.
On Saturday, the quiet working class neighborhood where the Garridos lived had transformed into a media circus of television trucks, wandering journalists and the simply curious, who began driving down the Garridos street once a police checkpoint into the neighborhood was removed. Some neighbors said they were growing wary of the constant questions of Mike Rogers, who owns a storage lot next to the Garridos' back fence said that he occasionally heard loud parties coming from the backyard. Rogers said the parties were a mostly male affair.
Phillip and Nancy Garrido are in jail, suspected of abducting Dugard 18 years ago and subjecting her to nearly a lifetime of torment in a squalid backyard compound. They pleaded not guilty Friday to a total of 29 counts, including forcible abduction, rape and false imprisonment.
Associated Press writers Lin in Sacramento and Terry Collin in San Francisco contributed to this story.
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