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.

The jury spent about a week deliberating the case. Jurors reached a verdict on four counts of first-degree murder on Friday, but the verdict was announced on Monday. The penalty phase of Merritt’s trial is set to begin on Tuesday.

Back in 2014, Merritt spoke to CNN and said he had “absolutely no clue” how the family was killed.

“If I were to guess, like anyone else, I would think it was probably random because I honestly don’t believe that family had anything to do with it. I don’t think that any of his friends had anything to do with it. Joseph was just too well-liked,” Merritt told CNN then.

Merritt said he and Joseph McStay were business associates who became friends. Merritt made custom indoor waterfalls and McStay would buy them, he said. They met in 2007 when McStay needed some help with a water feature. They played paintball together, had dinner a couple times a week, and he also spent time with the McStays and gotten to know the family, he said.

Merritt and McStay met for a business lunch in Rancho Cucamonga the day the family disappeared, he said.

“I am definitely the last person he saw,” Merritt said.

CNN’s Michael Pearson contributed to this report.