(CNN) The man accused of killing a California couple and their two children and burying them in the Mojave Desert was found guilty of first-degree murder on Monday.

Charles Ray Merritt, 62, could face the death penalty for killing the McStay family, who went missing in 2010.

The bodies of Joseph and Summer McStay and their sons, Gianni, 4, and Joseph Jr., 3, were found in a shallow grave in 2013, about 100 miles north of their suburban San Diego home. They were bludgeoned to death with a sledgehammer and buried in shallow graves outside Victorville.

Merritt, a business associate of Joseph McStay, was arrested in 2014. Prosecutors say Merritt owed McStay more than $42,000.

The family's disappearance had puzzled investigators, who said there were no signs of struggle at their home. Food had been left out and the dogs were home.

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