Inside the Standoff in a Nudist Ranch Bunker that Led to the Capture of Man Accused of Killing Couple (Exclusive)

It started with a call to the police on Thursday, Aug. 29.

The caller indicated that a family member Michael Sparks, who lived at the Olive Dell Ranch RV Park and Resort, confessed to killing two unnamed people and had threatened to die by suicide.

When the call came in, the Redlands police were canvassing the nudist resort in the foothills of the San Jacinto Mountains near Redlands, Calif., after two long-time residents, Dan Menard, 79, and his 73-year-old wife Stephanie, disappeared from their mobile home four days earlier with their shih tzu, Cuddles. The couple’s Chrysler Sebring was found abandoned on the side of a road with the key still in the ignition.

“We were out there following up, doing another canvas of the neighborhood,” Redlands Police spokesperson Carl Baker tells PEOPLE. “And while that team was out there on the site, that's when we received a call from a person who indicated that they were a family member of Michael Sparks and that he had told them, the family member, that he had killed two people and was going to commit suicide. He didn't say it was the Menards, but he said he had killed two people and was planning to commit suicide.”

Baker says authorities quickly locked down the entire ranch community and made several attempts to contact Sparks, who was the next door neighbor of the couple, without any response.

"They were making announcements over a loudspeaker," says Baker. "We believed he had weapons and that he had barricaded himself. We had been told that he had built a basement."

After several hours, authorities broke a window and sent in a Redlands Police Department drone to do a remote search of his mobile house. The drone was unable to see whether Sparks was in there.

At that point, Baker says, authorities brought in an armored vehicle with a hydraulic battering ram to break down the front wall.

“We used that to make entry to the house, pulled off the front wall,” Baker says. “There was some consideration that he had booby-trapped it, but we determined that the [armored vehicle] would've set off any kind of booby traps.”

Police says Sparks was hiding in a concrete bunker he had built underneath his residence.

The bunker, says Baker, was “a little more than five feet deep, you could walk down there, but you might have to stoop. It ran the length of the mobile home, the length and width of the mobile home.”

Sparks — who tried to shoot himself with a rifle, only to have it misfire — was at the entrance of the bunker when he was taken into custody.

Baker says a city sanitation crew then used a camera that checks for sewer blockages to look down into the basement.

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“They could see that there were bags of something in there, and we determined that they were most likely human remains,” he says.

A fire department team eventually recovered Stephanie's and Dan's remains. 

Both died from blunt force trauma to the head, according to the coroner.

“There’s been no sign of Cuddles,” says Baker.

Referencing the murders, Baker says authorities “believe it happened there on the property. His property or their property.”

Authorities have declined to comment about a motive behind the slayings.

“It’s a nightmare,” says friend and neighbor Tony Wiley, 69. “You hear stuff like this on the news, but you never imagine in a lifetime that it would be one of your friends, and in such a bizarre way.”

The couple’s friend Michelle Ann Archambault Reese adds, "They had a great little home for the two of them and their dog. They were just somebody you wanted a hug from. They were just wonderful people.”