2 Members of California Nudist Colony Found Dead, Next-Door Neighbor Arrested: 'It’s a Nightmare' (Exclusive)

At the Olive Dell Ranch RV Park and Resort, a nudist colony in the foothills of the San Jacinto Mountains near Redlands, Calif., longtime residents Dan and Stephanie Menard were friendly fixtures of the laid-back community.

Their neighbor Irene Engkraf, 78, played poker with Stephanie, 73, at the gated compound's clubhouse in the evenings and did Saturday Bible studies. A devout Christian, Dan, 79, organized the Easter and Christmas celebrations, and the couple attended church in nearby Moreno Valley, Calif.

So when the retired spouses failed to show up for church service on Sunday, Aug. 25, Engkraf took note. "That was not Stephanie and Dan," she says. "They would call and say, 'We're not feeling good,' or 'We're not going to go.' But they didn't." Concerned after spotting the couple's empty car parked at the side of a road with the key still in the ignition, Engkraf and another neighbor decided to enter the Menards' tidy mobile home at Olive Dell Ranch. Inside they found Stephanie's purse and wallet and the cane she always used. Her phone was beside a chair where she usually sat, and the house lights and a fan were on—but there was no sign of the Menards or Cuddles, the couple's feisty shih tzu.

"At that point," recalls Engkraf, "I said, 'Call the police.''

Law enforcement soon arrived on the scene, and a search for the missing Menards was launched. As the San Bernardino and Riverside County sheriff's departments and the Redlands police department deployed a bloodhound, helicopters and drones to scour the surrounding hills, Olive Dell residents, some of them on horseback, searched and distributed leaflets.

"We put out flyers of a picture of Dad, Stephanie and Cuddles together," says Engkraf.

"Everybody was worried because that wasn't like them," says Olive Dell Ranch resident Tony Garrett, 63. "I never saw Stephanie without her cane or phones. That's what worried everybody because that wasn't normal for her."

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Then, a call to the police that changed everything.

On Thursday, Aug. 29 authorities learned from a family member that neighbor Michael Sparks, 62—who had reportedly argued with the Menards over the pruning of a tree that shaded both of their properties—had confessed to killing two unnamed people and threatened to die by suicide.

"On Thursday, we had a team that was going back out there, canvassing the neighborhood again and continuing to search," 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 [die by] suicide. He didn't say it was the Menards, but he said he had killed two people and was planning to [die by] suicide."

Baker says authorities made several attempts to contact Sparks at his home without any response.

"They were making announcements over a loudspeaker," says Baker. "We broke a window and sent in a Redlands Police Department drone to do a remote search of his house after obtaining a search warrant. The drone was unable to see whether he 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 of Sparks' mobile home. "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 said Sparks was hiding in a concrete bunker he had built underneath his residence. After attempting to shoot himself with a rifle that misfired, Sparks was taken into custody by the Redlands police.

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

"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. It wasn't like he did it a mile away and then brought them back to his house. It happened right there. Part of that general area."

"We don't think that they were being held captive or anything like that," he says.

Baker says authorities searched the Menards' home an learned "that they had clearly left or not intended to leave the house because the computer was on, the air conditioning was on, and the purse was there, the cell phones were there. All of that indicated that they were not intending to leave."

Baker adds, "But other than that, there was nothing suspicious in their house. There was no indication of any kind of a struggle or anything like that."

"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."

Olive Dell Ranch — which boasted such amenities as a pool, jacuzzi and fun nights at the clubhouse including karaoke — seemed like the perfect place for the Menards to spend the rest of their lives. After raising two children and Dan spending his career working in the aeronautics industry in California, the Menards moved to the nudist ranch some 15 years ago and settled in quickly.

"They just enjoyed that type of lifestyle," says longtime friend Jody Padfield, 69. "It was a joke with us. They'd say, 'Well, you can come join us [at the ranch],' and I'd be, 'Oh yeah. Right.'" While Stephanie remained active in the community, driving down to the clubhouse in her golf cart to play bingo and poker, spending time at the laundromat, and occasionally lunch with friends, Dan, who had recently been diagnosed with dementia, mostly stayed at home with Cuddles at his feet and tinkered with his model-train collection and computer.

"They had a great little home for the two of them and their dog," says the couple's friend Michelle Ann Archambault Reese. "They had a beautiful outside patio area to kick back at. They were just somebody you wanted a hug from. They were just wonderful people."

The couple, she says, "were so in love with each other. There's nothing you can say bad about Dan and Stephanie."

The couple's longtime next-door neighbor Sparks—known in the community as Sparky—appeared to be more of a loner. "You'd see him once in a while, but mostly he liked his hot tub," says Garrett. "He wasn't a bad guy. He was no different than the other residents. Just a little more quiet, a little more reserved."

Tammie Wilkerson, 61, who also lives near Sparks, says he once offered to build a dog run for her four dogs and would often sit outside late into the night. "He said he hated the 'textile world' and that he had always been a nudist from as long as he could remember," she says. Although police have not specified a motive for the alleged killings, friends of both the Menards and Sparks say the neighbors had a misunderstanding about a tree.

"I've talked to them, and I know they had an issue about a tree getting cut because of branches going over to the Menards' place," says Garrett. "But, I can't say that's all of it. I can't say it's just one thing."

"When I first got here, he was telling me which neighbors he liked, which neighbors he could do without, and then he pointed in their direction, he goes, 'And I hate those f-ers,'" says Wilkerson. "I'm like, 'Dang, Sparky, that's a little rough.' And that's when he told me the tree thing. I was thinking it's a lot to hate somebody. There may be other reasons. I don't know. Only he knows."

"I don't know if that's what caused this or if he just snapped one day," she says. "I really don't know."

Padfield says Stephanie mentioned the feud on the phone months before the slayings. "She was talking about Dan, and I said, 'Well, what does he do [these days]?' She goes, 'He butts head with the neighbor next door.'"

As Sparks—who was charged and subsequently pleaded not guilty to the double murder—awaits trial at the West Valley Detention Center, residents of Olive Dell Ranch are missing the popular couple.