62-year-old neighbor arrested on suspicion of murder in connection with the disappearance of an elderly couple from a California nudist ranch

The neighbor of an elderly couple who disappeared from their home on a nudist ranch in California over the weekend has been arrested on suspicion of murder.

Stephanie Menard, 73, and her husband, Daniel Menard, 79, were reported missing by a friend on Sunday. They were last seen the morning before at their home in the 26000 block of Keissel Road on Olive Dell Ranch in Redlands, Redlands police said. The ranch is an RV park touted as a “family-friendly nudist resort” in Southern California.

Police said they found the couple's unlocked vehicle down the street from their home on Sunday. They also found Stephanie Menard's purse in their home, along with her and Daniel's cell phones. The couple's dog – a small white Shih Tzu named Cuddles – was also missing. Authorities described Daniel Menard as suffering from dementia and diabetes.

On Friday morning, police announced that her neighbor, 62-year-old Michael Royce Sparks, was arrested Thursday evening in connection with her disappearance and booked into the West Valley Detention Center on murder charges.

During an investigation at the ranch on Thursday, investigators learned “that a possibly involved person was on site” and authorities were trying to locate him, police wrote in an update on Facebook.

Investigators tried to reach the person at home for several hours but received no response. Police eventually used a TAC-CAT, an armored Caterpillar tractor used by police, to enter the person's home and conducted a search using remote video equipment, but were unable to locate anyone.

Sparks was eventually found under the house and taken into custody, NBC Los Angeles reported.

“We have not found the Menards, but investigators believe their bodies are on the property,” Redlands spokesman Carl Baker told NBC News on Friday.

Authorities did not disclose what led them to suspect Sparks of the murder or what the motive might have been. It is not immediately clear whether Sparks has retained an attorney.

Police were at Spark's home on Friday morning to “prepare to search for the couple's bodies,” but due to “significant damage,” the building had to be “secured” before search crews could enter the house.

This article was originally published on NBCNews.com.