Investigators were searching Old River and looking through trash on Thursday as part of an ongoing effort to find an 8-year-old Tracy girl missing since Friday afternoon, police said.
Police were also sifting through more than 560 leads for any information that may lead them to Sandra Cantu, adding that no suspects have been named in connection with the disappearance. She was last seen last Friday.
"We haven't ruled anybody out at this point," police Lt. Jeremy Watney said during a news conference on Thursday morning.
The little girl's father told police he will voluntarily undergo a lie detector test.
Daniel Cantu said he will do anything to help find his daughter.
"She's only eight years old. She's small, she's alone, she's scared." Cantu said. "And I love her very much. And if she can get to a phone, please run, dial 911. Do what you need to do, honey."
At the same time, Cantu says, he is frustrated and upset. Cantu says authorities in Mexico raided his home there and threateed his new wife.
Volunteers and police are going through the trash at a waste facility as the search continues.
A Tracy police spokesman says the search at the facility, about seven miles from the mobile home park where Sandra lives with her family, is routine.
Crews using bulldozers and other equipment are expected to be sifting through trash at the site all week.
There is still no sign of Sandra.
Investigators say they have received about 500 tips so far, but none of the tips indicate the girl may not be alive.
Police have identified two men they consider "persons of interest," though no arrests have been made.
Sandra was wearing a pink "Hello Kitty" T-shirt, a striped skirt and black leggings when she disappeared.