Police continued their search for a missing truck driver on Friday, digging in the backyard of an Ontario, Calif.,  home, searching for evidence. Oscar Javier Contreras Escobar was reported missing on Sept. 4 last year, days after he was last seen on Aug. 28, when he was dropped off by someone to meet with a female friend at the house policed searched on Friday.

Officers used a backhoe, cadaver dogs and a Bobcat machine to break up concrete in the yard on Thursday. The connection between Escobar and the owner of the house was not released, but investigators told KABC-TV  that some evidence has already been recovered.

“The initial focus was on the inside, the interior of the house, and for the last day or day-and-a-half or so, they’ve been focusing on the backyard area,” said Ontario Police Sgt. Dave McBride. “I wouldn’t specifically say we’re looking for body parts, but of course, in this type of investigation, that’s always a consideration.”

As many as 20 people were working in the backyard at once, searching on their hands and knees, digging. Detectives knew of the house in November but weren't able to obtain a search warrant until last week. They indicated something with “strong evidentiary value” had been recovered but would not elaborate.

“I've been told by detectives that these items are probably of such great value that they decided to bring out additional coroner personnel to help with the recovery of the items,” McBride said, while adding that work would continue on Saturday. “They're in there quite a ways. Who's to say how deep these items that we're looking for are buried, so we don't want to walk away thinking that we might have left something of importance.”

Escobar was described as a Latino man standing at 5 feet 5 inches tall and weighing 135 pounds. He has brown eyes and a bald head and was last seen sporting a mustache and goatee. Detectives said his ATM account had been used since the truck driver went missing.

Neighbors weren’t surprised when police suspected foul play at the house as they said that police had visited the house with a warrant many times before.

“It’s been raided about five times in 10 years. It was raided a few months ago,” one man who wished to remain anonymous told KTLA in California. “Activity left and right … day and night. This doesn’t surprise anybody that something has happened here.”