Disturbing new details in shocking double murder of nudist couple living on hedonistic bunker

California police have revealed disturbing new details about their standoff with a man accused of killing an elderly nudist couple.

Daniel Menard, 79, and his wife Stephanie, 73, were reported missing after they failed to show up at church on August 25, prompting Redlands police officers to scour the area around their home at the Olive Dell Ranch nudist resort for any signs of the couple.

But on the fourth day of their search, police received a phone call from someone claiming to be a relative of the couple's next door neighbor, Michael Sparks, 62. 

The caller claimed Sparks confessed to them that he had killed two unarmed people as he threatened to also kill himself, Redlands police spokesman Carl Baker recently told PEOPLE. 

'He didn't say it was the Menards, but he said he had killed two people and was planning to commit suicide,' Baker recounted of the phone call.

He said the police department immediately put the entire community on lockdown, as officers made several attempts to contact Sparks - but to no avail.

'They were making announcements over a loudspeaker,' Baker said of the officers at the scene. 

There was concern, however, that Sparks had barricaded himself inside the home with a cache of weapons, after officers learned he had built an underground bunker. 

So, after several hours of no response, authorities broke a window and sent in a Redlands Police Department drone to conduct a remote search of Sparks' mobile home - which was unable to locate Sparks inside, Baker said.

Police then brought in an armored vehicle with a hydraulic battering ram to break down the front wall of his home.

'We used that to make entry to the house, pulled off the front wall,' Baker said.

'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 ultimately found Sparks hiding in his concrete bunker, which Baker said 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,' he said.

Sparks was right at the entrance to the bunker, and tried to shoot himself with a rifle that misfired when he was taken into custody.

In the aftermath, city sanitation crew members used a camera designed to check for blockages in the sewer system to get a look at Sparks' basement.

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

Those remains were then recovered by members of the fire department, and were confirmed to be those of the Menard's.

The San Bernardino County Coroner later determined that they both died of blunt force trauma to the head, and ruled their deaths a homicide.

Baker said police now believe they were killed on their own property, adding that officers were never able to recover their beloved Shih Tzu, Cuddles, whom they were last spotted with.

A motive for the killings remains unclear but onlookers have said there was some tension between Sparks and the Menards, with neighbor Tammie Wilkerson saying Sparks had an ongoing dispute with the couple.

‘He didn't like them. He hated them, and he told me many times,’ Wilkerson told CBS News. 

‘It's such a stupid reason. They had a tree that was on their property line and Dan used to go trim the limbs and he hated that. That formed his hatred towards them.’

Sparks is now charged with two counts of murder and two special circumstance allegations in connection with the Menards' deaths.

He has pleaded not guilty.