SAN BERNARDINO, Calif. » Authorities have kept quiet for months about what drove them to charge a California man with killing a family of four and burying their bodies in shallow desert graves.

But San Bernardino prosecutors on Monday are expected to finally reveal the case they’ve been building against 58-year-old welder Charles "Chase" Merritt for the murders of his business partner, Joseph McStay, the man’s wife and their two young sons.

Merritt, who was arrested last November, has pleaded not guilty to quadruple murder. After a preliminary hearing, a judge will decide whether there is enough evidence to hold a trial.

The McStay family vanished in February 2010, puzzling investigators who said there were no signs of forced entry at the home, nothing was missing, and the couple’s credit cards and tens of thousands of dollars in bank accounts were untouched.

More than three years later, the family’s remains were found 100 miles from their Fallbrook home in San Bernardino County.

Prosecutors declined to discuss the case before Monday’s preliminary hearing, and authorities have not released details of the deaths of McStay, 40; his wife, Summer, 43; and their sons, 4-year-old Gianni and 3-year-old Joseph Jr.

Merritt’s lawyer, Jimmy Mettias, said he expected prosecutors to allege his client used a sledgehammer to kill McStays after a business dispute and covered up his tracks by painting the family’s house and burying his victims and the weapon in the desert.

Mettias said nothing on the sledgehammer could be traced to Merritt, and questioned prosecutors’ ability to link his client to the crimes.

"We have serious issues with the state of the evidence," he said. "I could see where they chose, OK, we’re going to go with this guy, but nothing that is going to prove his guilt."

Mettias said he expected prosecutors would say Merritt took money from McStay’s business building indoor water features, prompting a confrontation between the men.

Mettias said his client had an alibi, but he would not reveal it before trial.