The father of a missing 8-year-old California girl pleaded with her to "scream, kick, do what you need to do" to escape her captors as police sifted through trash for signs of the child.
Detectives also planned water searches of an area lake for much of Thursday, they told reporters.
Sandra Cantu's dad Daniel said he has spoken at length with police.
"I've just gotten through a couple hours of being interrogated," Cantu told FOX San Francisco affiliate KTVU.
The missing child's father will be re-interviewed, said Tracy Police Lt. Jeremy Watney. He declined to comment on whether the father had taken a polygraph.
"He's scheduled to come in and talk to us again today," Watney said at a news conference.
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Daniel Cantu is divorced from Sandra's mother and lives in Mexicali, along the California border with Mexico. He hasn't seen his daughter in a year, he told KTVU, but he does want to get a message to her.
"Honey, if you can get to a phone, dial 911, babe," the station quoted him as saying. "Scream. Kick. Do what you need to do."
Cantu said he hadn't taken Sandra to Mexico.
On Thursday, investigators combed through garbage at a landfill in Tracy, Calif., but turned up no clues.
The facility is about seven miles from where Sandra lives with her family in Orchard Estates Mobile Home Park near Interstate 205.
The search of the trash is routine, according to police.
"We are going through absolutely everybody’s trash in this city of Tracy this week," Watney told reporters. "It’s just covering a base. If we don’t do it now, we won’t be able to do it later."
Crews using bulldozers and other equipment were expected to be sifting through the garbage at least through Thursday and possibly through the end of the week.
Detectives hadn't gotten any information leading them to the landfill, he added — nor did they have any tips connected to the lake they planned to search between 10 a.m. and 3 p.m. PDT.
"Nothing has pointed us in that direction," he said. "It's just one of those things we're doing."
The girl was last seen at about 4 p.m. on March 27, when a surveillance video camera recorded her walking away from her family's mobile home in Tracy. Her mother, Maria Chavez, reported her missing at about 8 p.m.
Investigators said they have been poring over more than 539 leads in their search for the child, but none of the tips indicate Sandra is dead.
"We're not ruling anything out, because the moment we do is when we're proven wrong," Watney told KTVU. "We're going to treat it as a missing person, as a runaway, possibly foul play."
To date, four vehicles have been towed away from the mobile home park. Four trailers there have been searched, as well as two other locations, according to Watney. Detectives have scoured footage from surveillance cameras pointed at the front entrance of the park.
Police say they're investigating two men in the case, but Watney cautioned against calling them persons of interest or suspects.
One of the men was questioned after allegedly obstructing parts of the investigation, according to Watney.
Police talked to the other after learning of an incident two years ago when he reportedly kissed then 6-year-old Sandra on the mouth in a swimming pool.
Click here for a video report from KTVU.com about the kissing incident.
The men's homes have been searched and their vehicles confiscated, and the evidence collected is undergoing forensic analysis.
Sandra's family held another vigil for the girl in their trailer park Wednesday night.
The child is described as Hispanic, 4 feet tall and weighing 45 pounds, with brown hair and brown eyes. She was wearing a pink Hello Kitty T-shirt and black leggings when she was last seen.
The Associated Press contributed to this report.
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