Volunteers said they would be back Sunday morning and added that their search could last a full week because so far, no new evidence has been found.
"There's a lot of debris here. It is very time consuming," Doreen Mathews with the Hercules Police Department said Saturday.
Sifting through 1 acre of land and 3,000 tons of trash is taking days. The Keller Canyon Landfill is the strongest lead so far.
"We are looking for anything that will lead us to Frederick Sales," Mathews said.
Sales is still missing. His father, Ricardo Sales, was found bludgeoned to death inside a Hercules home last Saturday and that was also the last time anyone saw Frederick. The owner of the home is Cindy Tran. She is Efren Valdemoro's girlfriend and she is dead too.
Police believe Valdemoro attacked Ricardo Sales and his son because he felt one of them might be involved with Tran. Police also think Valdemoro strangled his girlfriend before he was shot to death in a confrontation with police last Tuesday night.
Now four days later, investigators still need answers and they are hoping to find them at the landfill. 15 search and rescue volunteers and one cadaver dog have been sifting through debris inch-by-inch.
"You have to search small areas at one time with the dog. It's very difficult becuase there are very many difference scents," Mathews explained,
The only other place police have to turn is the Solano County lock up, where Charles Rittenhouse is being held. The 72-year-old knows Efren Valdemoro, who used to stay with Rittenhouse and his wife, Segundina Allen.
Vallejo police found Allen and her friend, Marcaria Smart, dead on Tuesday. Rittenhouse is charged only with having large amounts of explosives in the house and his attorney says Rittenhouse is not involved with any murders.
"I have reason to believe the bodies were just put there some time that day, Tuesday, the day of his arrest," his attorney Leslie Prince said.
The reason police have gone to the landfill is because the car Valdemoro was seen driving, which also happened to belong to Segundina Allen, was dumped at a Hercules shopping center. Valdemoro used to work at that same shopping center and all the trash from that center goes to the Keller Canyon Landfill.