A business associate was arrested in the murders of a family of four, including two young boys, whose disappearance from their San Diego County home in 2010 was a mystery until their remains were discovered in graves in the California desert last year, officials said Friday.

San Bernardino County Sheriff John McMahon identified the suspect as Charles Merritt, 57, who was due in court later in the day to face four counts of murder.

The lengthy investigation revealed that Joseph McStay, 40, his wife, Summer, 43, and their sons, 4-year-old Gianni and 3-year-old Joseph, were killed in their home in Fallbrook and all were victims of blunt-force trauma, the sheriff said.

Authorities refused to discuss a motive or any details of how the family was killed or evidence found at the home or the shallow desert gravesite.

"Our job is to look at everyone and eliminate who we could and see where this was going to take us and it led us to him," San Bernardino sheriff's Sgt. Chris Fisher said of Merritt.

Joseph McStay had a business designing and installing home water features. Investigators said he had asked Merritt to design some special waterfalls and the two met at a restaurant on the day the family is believed to have been killed.

Merritt's name surfaced previously in the investigation. In 2011 it was reported that Joseph McStay's last cellphone conversation was with Merritt.

The couple and their boys vanished in February 2010 from Fallbrook.

A year ago, their skeletons were found in the desert outside Victorville. The site was not far from heavily traveled Interstate 15, which connects San Diego and Las Vegas.

Investigators said there were no signs of forced entry at the family's home or in their SUV, which was found parked near the U.S.-Mexico border. Nothing was missing from the home, and the couple's credit cards and tens of thousands of dollars in bank accounts never were touched.

Investigators in San Diego County, who had the case until the bodies were found in San Bernardino County, previously said it appeared the family fled the home at a moment's notice, with eggs on the counter and bowls of popcorn in the home.

Fisher said detectives now believe the family was killed in the home.

A grainy surveillance video that investigators thought might have shown the McStays walking across the border into Mexico is not the family and is not related to the case, he said.

Investigators in San Bernardino County found evidence with the bodies that helped them solve the case but stressed there was no smoking gun. Merritt was one of the associates that San Diego investigators had looked at and his name was passed along to San Bernardino County investigators when they took over the case, Fisher said.

Over the course of the investigation they interviewed Merritt several times and tracked him as he moved to different locations around Southern California, but the case was primarily built by reviewing the San Diego County investigation and re-interviewing hundreds of people.

McMahon said his team reviewed 4,500 pages of material from San Diego County, served 60 warrants, got 250 tips and did 200 interviews.

Merritt was arrested Wednesday in the Chatsworth area of Los Angeles.

Fisher said Merritt has previous felony convictions and has served time in state prison.