A look inside the standoff in a nudist ranch bunker that led to the arrest of a man accused of killing a couple (Exclusive)

Michael Sparks, 62, was charged with two counts of murder in the deaths of Dan and Stephanie Menard

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

The caller indicated it was a family member Michael Vonkenwho lived at the Olive Dell Ranch RV Park and Resort, confessed to killing two unnamed people and threatening to commit suicide.

When the call came in, Redlands police were investigating the nudist resort at the foot of the San Jacinto Mountains near Redlands, California, after two longtime residents Then Menard79, and his 73-year-old wife Stephaniedisappeared 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 tracking and creating another canvas of the neighborhood,” Carl Baker, spokesperson for the Redlands Police Department, tells PEOPLE. “And while that team was on scene, we received a call from an individual indicating that they were a relative of Michael Sparks and that he had told them, the relative, that he had killed two people and was going to kill himself. He didn’t say it was the Menards, but he said he had killed two people and was planning to kill himself.

Related: 2 California Nudist Colony Members Found Dead, Neighbor Arrested: ‘It’s a Nightmare’ (Exclusive)

Baker says authorities quickly locked down the entire ranch community and made several attempts to contact Sparks, the couple’s neighbor, without any response.

“They were making announcements over a loudspeaker,” Baker said. “We thought he had weapons and that he had barricaded himself. We were told he had built a cellar.”

After several hours, authorities broke a window and sent a Redlands Police drone to remotely search his mobile home. The drone couldn’t see if Sparks was in there.

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

“We used that to gain access to the house, it was pulled off the front wall,” Baker says. “There was some consideration that he had set a booby trap, but we came to the conclusion that the (armored vehicle) would have set off any kind of booby trap.”

Related: Elderly couple living at Nudist Ranch died of blunt force trauma to the head: Coroner

Police say Sparks hid in a concrete bunker he built underneath his home.

The bunker, Baker says, was “a little over five feet deep, you could walk down it, but you might have to duck. 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 but failed – was at the entrance to 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 into the basement.

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

A fire team eventually recovered Stephanie and Dan’s remains.

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

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

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

Authorities declined to comment on the motive behind the killings.

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

The couple’s friend, Michelle Ann Archambault Reese, added, “They had a great little house for the two of them and their dog. They were just someone you wanted to hug. They were just wonderful people.”