Suspect told CNN: I have no clue

• Chase Merritt told CNN in January that he met Joseph McStay in 2007


• They did business together but they were also close friends, Merritt says


• He was the last person to see McStay the day he, his wife and two kids vanished, he told CNN


• Police believe Merritt, acting alone, killed the four family members in their home

Watch "Buried Secrets: Who Murdered the McStay Family?" Tuesday at 9 p.m. ET on CNN.

(CNN) -- Earlier this year, CNN asked a good friend and business associate of Joseph McStay what he thought happened to the California salesman and his family.

How did Charles "Chase" Merritt think they were killed?

"I have absolutely no clue," Merritt told CNN in an exclusive television interview in January.

Police believe he does. On Wednesday, they arrested Merritt, 57. He is charged with four counts of murder in the deaths of McStay, his wife Summer and their two small boys.

The family disappeared from their home in northern San Diego County in February 2010. Their remains were found a year ago, in shallow graves in the Mojave Desert, about 100 miles north of their home.

The discovery ended the mystery of what happened to the McStays. But who killed them, and why?

'Cold and callous' murders of McStay family solved, authorities say

"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 in January.

Announcing the arrest Friday, authorities in San Bernardino County said they believe the family died of blunt force trauma inside their home, but they declined to discuss specifics of the deaths or a motive.

"I am definitely the last person he saw," Merritt told CNN

Hear what McStay suspect told CNN

Suspect arrested in McStay killings

In his interview with Kaye, Merritt said he and McStay were business associates who became friends. Merritt made custom indoor waterfalls and McStay would buy them, he said. They had met in 2007 when McStay needed some help with a water feature.

They played paintball together. They had dinner at Merritt's place a couple times a week, he said. Merritt helped him move.

He'd 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.

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

He told CNN they were also on the phone constantly, perhaps 12 to 13 times that day.

There was another call from McStay's phone to Merritt the night of February 4, 2010. It came about 40 minutes after a neighbor's security camera captured the family's Isuzu pulling out of their cul-de-sac. Merritt didn't answer.

Merritt told he told CNN's Kaye in January he was watching television with his then-girlfriend and he picked up the phone, looked at it and set it back down. He was tired. He called back the next day, he said.

Was that just a regular call from his friend, or could it have been a call for help?

"There are hundreds of scenarios. I have gone over all of them in my head," he said. "Of course I regret not picking up the phone."

The disappearance of the McStays

Merritt was questioned by police after the disappearance. They just asked him the "standard questions," he said.

He also claimed to have taken a polygraph test.

What did it show?

"I don't know," he said. "Apparently -- I mean I haven't -- after I took the polygraph test, law enforcement has not contacted me at all since. So, I kind of simply assumed: Well, apparently that resolved the issues that they may be looking at with me."

Merritt said he didn't recall the police directly asking him if he killed the McStays. That was because at the time it seemed they were four people who left on their own volition, he said.

Lucrative waterfall project lay ahead, Merritt told CNN

Police had never named Merritt as a suspect before Wednesday's arrest.

He has served time in prison, according to criminal records from California, but none of the crimes involved violence.

According to the Los Angeles Times, Merritt spent most of his life working with his hands. He received a metalworking license in 1982.

At their lunch the day of the disappearance, Merritt said, he and McStay talked business -- just business. They were working on a waterfall project for a Saudi couple and Merritt said there needed to be a large check written to a stainless steel company that was doing work for them.

McStay seemed happy. On the horizon was another project that would involve 500 waterfalls. Each one would sell for $17,000 or $18,000 -- as much as $9 million total -- but McStay still needed to sign the contract.

"It was pretty much a done deal," Merritt said.

San Bernardino authorities said Friday that after reviewing 4,500 pages of investigative records, executing 60 search warrants and conducting 200 interviews, they believe Merritt acted alone.

He appeared in court on Friday, but his arraignment was postponed until next Wednesday. His lawyer, Robert Ponce, left court without speaking to reporters.

CNN's Jessica Small, Melissa Dunst and Jack Hannah contributed to this report.