(CNN) Five years ago, the McStays were living the California dream. The family had moved into a new home in Fallbrook, and Joseph McStay's business was taking off.

He had started a company called Earth Inspired Products that sold waterfalls, and online orders were strong.

McStay connected with Chase Merritt , who manufactured custom indoor waterfalls. The two quickly bonded.

"We talked constantly. ... He came down and had dinner with me and my family once or twice a week virtually every week," Merritt told CNN's Randi Kaye . "Joseph was my best friend."

It's a surprising statement considering where Merritt is now -- behind bars, charged with murder in the deaths of McStay; his wife, Summer; and their two small children, Gianni and Joseph Jr.

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The last time anyone heard from the McStay family was February 4, 2010. For years, no one knew what happened to them.

Police who searched their home days after the family disappeared found eggs on the kitchen counter and bowls of popcorn in the living room, along with the family's two dogs. There were no signs of a struggle.

The bodies of the McStay family were found in the Mojave Desert in November 2013. Police say they believe the family died of "blunt force trauma."

Merritt, who is now representing himself, has pleaded not guilty. A preliminary hearing has been set for April 7. No trial date has been scheduled yet.

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But investigators are confident they have the right man.

From the start of the case, San Bernardino County detectives had their eyes on Merritt, a talented welder who was known for his laid-back, cowboy demeanor.

Joseph McStay's father, Patrick, teamed up with Gina Watson, who knew his son through work. The two did their own investigating and came across what they say are some troubling inconsistencies.

Merritt has said he was the last person to see McStay alive.

The two, Merritt said, met for a business lunch in Rancho Cucamonga the day the family disappeared.

"I am definitely the last person he saw," Merritt told Kaye in January 2014.

Asked if McStay was concerned about anything, Merritt said, "No, no, no. He seemed happy."

But Patrick McStay told CNN that Merritt told him Joseph was upset about a damaged fountain Merritt built for him.

Joseph McStay also told his father he was frustrated with Merritt's work.

"Joey had talked about the quality of some of the fountains had slipped. And Joey wasn't happy with that," Patrick McStay said. "Because he was getting complaints."

Joseph McStay had talked to his father about getting another welder.

Merritt also told CNN about receiving a call from McStay the night he disappeared.

Merritt said he didn't remember the call until his then-girlfriend reminded him about it. The call came, he said, when they were watching television. Merritt picked up the phone, looked at it and set it back down. He was tired, he said.

But when Patrick McStay asked about the call, Merritt said it was a follow-up to their conversation at lunch.

San Bernardino County District Attorney Michael Ramos said he can't yet say what the motive was, but he said his team had been watching Merritt on a daily basis.

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"We know there have been many inconsistencies," Ramos said. "His story is all over the place."

Still, the case against Merritt may have holes. Merritt told CNN he went to the McStay house after the family went missing and before it was sealed off.

Officers believe the McStays were killed in the home, but 11 days passed between the family's disappearance and an alert to the sheriff's department. It took San Diego investigators three days to obtain the warrants they needed to complete a full search, and during that time, the home remained unsealed.

How reliable is evidence gathered at the McStay house so many days after investigators say the family was killed there? Could one person kill a family of four and bury the bodies 100 miles away?

And the fact that it has been five years since the family went missing does not make the prosecution's case any easier.

"I think the biggest obstacle ... is time. Because witnesses forget, people forget the time frames, what occurred, etc.," Ramos said.