REDLANDS, Calif. (AP) — A Southern California couple whose bodies were found under their neighbor’s home in a nudist ranch died from “blunt force trauma to the head,” an autopsy found.

The San Bernardino County Sheriff’s Department released the cause of death of Daniel Menard, 79, and his wife Stephanie, 73, on Tuesday, the Los Angeles Times reported.

The couple and their dog were last seen on Aug. 24 and reported missing to the Redlands Police Department by a worried friend. Five days after they went missing, searchers found their remains in bags in a concrete bunker underneath the home of their neighbor Michael Royce Sparks. Sparks, 62, was arrested on homicide charges and pleaded not guilty during his arraignment on Sept. 9.

Authorities have not revealed a motive in the killings but a neighbor told local media that Sparks hated the couple and that they feuded over a tree between their properties.

″(Sparks) didn’t like the Menards,” neighbor Tammie Wilkerson told KTTV-TV. “He said it many times that he hated them, but I never thought he’d do something like this.”

The couple’s unlocked car was found near their residence in Olive Dell Ranch, and both their phones and Stephanie Menard’s purse were still inside their home. Daniel Menard was described as a diabetic with dementia.

Olive Dell Ranch is a family, and couples-friendly nudist resort in Colton, California, that is an “ideal spot to enjoy the nudist/naturist lifestyle whether visiting for the day or an overnight stay,” according to its website.